XXXVII  . and XXXVIII., which contain some See also:

• STATISTICS

statistics for See also:

• BATAVIA

Batavia due to See also:

• VAN

van Bemmelen, and some for See also:

• GREENWICH

Greenwich derived from the data in Maunders. papers referred to above . Table XXXVII. gives the relative frequency of occurrence for two See also:

• HOUR

hour intervals, starting with midnight, treating separately the storms of See also:

• GRADUAL (Med. Lat. gradualis, of or belonging to steps or degrees; gradus, step)

gradual (g) and sudden (s) commencement . In Table XXXVIII. the See also:

• DAY (O. Eng. dreg, Ger. Tag; according to the New English Dictionary, " in no way related to the Lat. dies")
• DAY, JOHN (1574-1640?)
• DAY, THOMAS (1748-1789)

day is subdivided into three equal parts . Batavia and Greenwich agree in showing maximum frequency of beginnings about the See also:

• TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
• TIME, MEASUREMENT OF
• TIME, STANDARD

time of minimum frequency of endings and conversely; but the See also:

• HOURS, CANONICAL

hours at which the respective See also:

• MAXIMA

maxima and minima occur at the two places differ rather notably . § 36 . There are peculiarities in the sudden movements ushering in magnetic storms which deserve See also:

• FULLER, ANDREW (1954-1815)
• FULLER, GEORGE (1822—1884)
• FULLER, M
• FULLER, MARGARET, MARCHIONESS
• FULLER, MELVILLE WESTON (1833-1910)
• FULLER, THOMAS (16o8-1661)
• FULLER, WILLIAM (1670--c. 1717)

fuller mention . According to van Bemmelen the impulse consists usually at some stations of a sudden slight jerk of the magnet in one direction, followed by a larger decided See also:

• MOVEMENT

movement in the opposite direction, the former being often indistinctly shown . Often we have at the very commencement but a faint outline, and thereafter a continuous movement which is only sometimes distinctly indicated, resulting after some minutes in the displacement of the trace by a finite amount from the position it occupied on the See also:

• PAPER
• PAPER (Fr. papier, from Lat. papyrus)

paper before the disturbance began . See also:

• TOTAL

Total Percentages . { Number . See also:

• WINTER, JOHN STRANGE
• WINTER, PETER (c. 1755-1825)

Winter . See also:

• EQUINOX (from the Lat. aequus, equal, and nox, night)

Equinox .

Summer . Greenwich disturbed days, all, 1848—1902 4,214 33'9 39'2 26.9 Greenwich disturbed days, range To' to 3o', 1848 1902 . . . 3,830 33'9 39.0 27.1 Greenwich disturbed days, range 30' to 6o', 1848 1902 • . . 307 34'5 41.0 24.4 Greenwich disturbed days, range over 6o', 1848 1902 . . . 77 29'9 41.6 28.6 See also:

• KEW

Kew highly disturbed days, 1 890—1900 . . . 209 38.3 41.6 20.1 Greenwich magnetic storms, all, 1848—1903 . 726 32.1 42'3 25.6 Greenwich magnetic storms, range 20' to 30', 1848—1903 . . . . 392 30.1 43.6 26.3 Greenwich magnetic storms, range over 30', 1848—1903 .

. . . 334 34'4 40'7 24.9 Greenwich m a g See also:

• NET

net i c storms, all, 14 years of S. max 258 35.3 38.0 26.7 Greenwich magnetic storms, all, 15 years of S. See also:

• MIN

min 127 28.4 48'0 23.6 Batavia magnetic storms, all, 1883—1899 . 1,008 32'9 34'9 32'2 Batavia magnetic storms of gradual commence- ment . . . . 679 32'4 34.8 32'8 Batavia magnetic storms of sudden commence- ment 329 33'7 35'3 31'0 This may mean, as van Bemmelen supposes, a small preliminary movement in the opposite direction to the clearly shown displacement; but it may only mean that the magnet is initially set in vibration, swinging on both sides of the position of See also:

• EQUILIBRIUM (from the Lat. aequus, equal, and libra, a balance)

equilibrium, the real displacement of the equilibrium position being all the time in the direction of the displacement apparent after a few minutes . To prevent misconception, the direction of the displacement apparent after a few minutes has been termed the direc- Hour. o 2 4 6 8 10 12 14 16 18 20 22 Beginning g 5 5 5 6 zo 16 7 5 6 9 8 8 S 7 5 7 IO IO II IO 8 8 9 8 7 Maximum ( g 12 10 6 5 4 9 9 6 6 6 12 15 S 14 7 5 2 2 9 9 5 8 10 13 16 End all 15 16 , 19 13 5 3 6 5 4 5 4 5 tion of the first decided movement in Table XXXIX., which contains some data as to the direction given by See also:

• ELLIS (originally SHARPE), ALEXANDER JOHN (1814-189o)
• ELLIS, GEORGE (1753-1815)
• ELLIS, ROBINSON (1834- )
• ELLIS, SIR HENRY (1777-1869)
• ELLIS, WILLIAM (1794 – 1872)

Ellis 41 and van Bemmelen." The + sign means an increase, the — sign a decrease of the See also:

• ELEMENT (Lat. elementum)

element . The sign is not invariably the same, it will be understood, but there are in all cases a marked preponderance of changes in the direction shown in the table . The fact that all the stations indicated an increase in See also:

• HORIZONTAL

horizontal force is of See also:

• SPECIAL

special significance . See also:

• EPOCH (Gr. E7roxij, holding in suspense, a pause, from E1rxav, to hold up, to stop)

Epoch . Class . Total Percentages . Number .

1—8 p.m . 9 4 a.m. See also:

• NOON

noon . Begin- ` 1848—1903 all 721 60•, 21 9 I8 o 1882 -1903 276 580 188 23.2 mng lj sudden 77 45'4 27'3 27'3 ,, 1 848—19o3 all 720 9'4 44'6 46.0 End 1882—1903 7 z 41 7 51.1 sudden 276 77 11'7 35.1 53.2 § 37 . That large magnetic disturbances occur simultaneously over large areas was known in the time of See also:

• GAUSS, KARL FRIEDRICH (1777-1855)

Gauss, on whose initiative observations were taken at 5-See also:

• MINUTE
• MINUTE (Lat. minutes, small; minuere, to make less)

minute intervals at a number of stations on prearranged See also:

• TERM

term days . During See also:

• MARCH
• MARCH (1) (from Fr. marcher, to walk; the earliest sense in French appears to be " to trample," and the origin has usually been found in the Lat. marcus, hammer; Low Lat. marcare, to hammer; hence to beat the road with the regular tread of a soldier: cf.
• MARCH, AUZIAS (c. "1395-1458)
• MARCH, EARLS OF
• MARCH, FRANCIS ANDREW (1825– )

March 1879 and See also:

• AUGUST (originally Sextilis)

August 1880 some large magnetic storms occurred, and the magnetic curves showing these at a number of stations fitted with Kew See also:

• PATTERN

pattern magnetographs were compared by W . G . See also:

• ADAMS
• ADAMS, ANDREW LEITH (1827-1882)
• ADAMS, CHARLES FRANCIS (1807-1886)
• ADAMS, HENRY (1838— )
• ADAMS, HENRY CARTER (1852— )
• ADAMS, HERBERT (i858— )
• ADAMS, HERBERT BAXTER (1850—1901)
• ADAMS, JOHN (1735–1826)
• ADAMS, JOHN QUINCY (1767-1848)
• ADAMS, SAMUEL (1722-1803)
• ADAMS, THOMAS (d. c. 1655)
• ADAMS, WILLIAM (d. 162o)

Adams.42 He found the more characteristic movements to be, so far as could be judged, simultaneous at all the stations . At comparatively near stations See also:

• PLACE (through Fr. from Lat. platea, street; Gr. IrAar6s, wide)

Place . See also:

• DECLINATION (from Lat. declinare, to decline)

Declination . Horizontal Force . See also:

• VERTICAL (from Lat. vertex, highest point)

Vertical Force . See also:

• PAVLOVSK

Pavlovsk See also:

• WEST
• WEST, BENJAMIN (1738-1820)
• WEST, NICHOLAS (1461-1533)

West + + See also:

• POTSDAM

Potsdam West + — Greenwich West + + Zi-ka-wei See also:

• EAST
• EAST, ALFRED (1849- )

East + - See also:

• KOLABA (or COLABA)

Kolaba East + - Batavia West + - See also:

• MAURITIUS

Mauritius East + + Cape See also:

• HORN
• HORN (a common Teutonic word, cognate with Lat. cornu; cf. Gr. Kipas)
• HORN (Lat. cornu; corresponding terms being Fr. cor, trompe; Ger. Horn; Ital. corno)
• HORN, ARVID BERNHARD, COUNT (1664-1742)
• HORN, PHILIP DE MONTMORENCY, COUNT

Horn West + — such as Stonyhurst and Kew, or See also:

• COIMBRA

Coimbra and See also:

• LISBON (Lisboa)

Lisbon, the curves were in See also:

• GENERAL
• GENERAL (Lat. generalis, of or relating to a genus, kind or class)

general almost duplicates., At Kew and St See also:

• PETERSBURG

Petersburg there were usually considerable See also:

• DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences in detail, and the movements were occasionally in opposite directions .

The differences between See also:

• TORONTO

Toronto, See also:

• MELBOURNE
• MELBOURNE, WILLIAM LAMB, 2ND VISCOUNT (1779-1848)

Melbourne or Zi-ka-wei and the See also:

• EUROPEAN

European stations were still more pronounced . In 1896, on the initiative of M . Eschenhagen,43 See also:

• EYE
• EYE (O. Eng. edge, Ger. Auge; derived from an Indo-European root also seen in Lat. oc-ulus, the organ of vision (q.v.)

eye observations of declination and horizontal force were taken at 5-second intervals during prearranged hours at Batavia, See also:

• MANILA

Manila, Melbourne and nine European stations . The data from one of these occasions when appreciable disturbance prevailed were published by Eschenhagen, and were subsequently analysed by Ad . See also:

• SCHMIDT, H
• SCHMIDT, HEINRICH JULIAN (1818-1886)
• SCHMIDT, KARL VON (1817-1875)
• SCHMIDT, WILHELM ADOLF (1812-1887)

Schmidt.44 Taking the stations in western See also:

• EUROPE

Europe, Schmidt See also:

• DREW
• DREW, SAMUEL (1765-1833)

drew several See also:

• SERIES (a Latin word from serere, to join)

series of lines, each series representing the disturbing forces at one instant of time as deduced from the departure of the elements at the several stations from their undisturbed value . The lines answering to any one instant had a general sameness of direction with more or less divergence or convergence, but their general trend varied in a way which suggested to Schmidt the passage of a See also:

• SPECIES

species of vortex with large but finite velocity . The conclusion that magnetic disturbances tend to follow one another at nearly equal intervals of time has been reached by several See also:

• INDEPENDENT

independent observers . J . A . Broun45 pronounced for a See also:

• PERIOD
• PERIOD (Gr. irepioSos, a going or way round, circuit, aepi, round, and &Sis, way, road)

period of about 26 days, and expressed a belief that a certain See also:

• ZONE (Gr. 'WV77, a girdle, from 'wvvLvay to gird)

zone, or zones, of the See also:

• SUN
• SUN (0. Eng. sonne, Ger. sonne. Fr. soleil, Lat. sol, Gr. ijXior, from which comes helio- in various English compounds)

sun's See also:

• SURFACE

surface might exert a prepotent See also:

• INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence on the See also:

• EARTH
• EARTH (a word common to Teutonic languages, cf. Ger. Erde, Dutch aarde, Swed. and Dan. jord; outside Teutonic it appears only in the Gr. 'pq'e, on the ground; it has been connected by some etymologists with the Aryan root ar-, to plough, which is seen in
• EARTH, FIGURE OF
• EARTH, FIGURE OF THE

earth's See also:

• MAGNETISM
• MAGNETISM, TERRESTRIAL

magnetism during several See also:

• SOLAR, SOLLER (Lat. solarium, Fr.• galetas, Ital. solaio)

solar rotations . Very similar views were advanced in 1904 by E . W .

Maunder,39 who was wholly unaware of Broun's See also:

• WORK

work . Maunder concluded that the period was 27.28 days, coinciding with the sun's rotation period relative to an observer on the earth . Taking magnetic storms at Greenwich from 1882 to 1903, he found the See also:

• INTERVAL

interval between the commencement of successive storms to approach closely to the above period in a considerably larger number of instances than one would have expected from See also:

• MERE
• MERE, ADALBERT (1838-1909)

mere See also:

• CHANCE (through the O. Fr. cheance, from the Late Lat. cadentia, things happening, from cadere, to fall out, happen; cf. " case ")

chance . He found several successions of three or four storms, and in one instance of as many as six storms, showing his interval . In a later paper Maunder reached similar results for magnetic storms at Greenwich from 1848 to 1881 . Somewhat earlier than Maunder, See also:

• ARTHUR (Fr. Arius)
• ARTHUR, CHESTER ALAN (1830 – 1886)

Arthur Harvey46 deduced a period of 27.246 days from a See also:

• CONSIDERATION (from Lat. considerare, to look at closely, examine, generally taken to be from con-, and the base seen in sidus, sideris, a star, the word being supposed to be originally an astrological or astronomical term)

consideration of magnetic disturbances at Toronto . A . Schuster,47 examining Maunder's data mathematically, concluded that they afforded rather strong See also:

• EVIDENCE (Lat. evidentia, evideri, to appear clearly)

evidence of a period of about i (27.28) or 13.6 days . Maunder regarded his results as demonstrating that magnetic disturbances originate in the sun . He regarded the solar See also:

• ACTION

action as arising from active areas of limited extent on the sun's surface, and as propagated along narrow, well defined streams . The active areas he believed to be also the seats of the formation of sun-spots, but believed that their activity might precede and outlive the visible existence of the sun-spot . Maunder did not discuss the See also:

• PHYSICAL

physical nature of the phenomenon, but his views are at least analogous to those propounded somewhat earlier by Svante See also:

• ARRHENIUS, SVANTE AUGUST (1859– )

Arrhenius,48 who suggested that small negatively charged particles are driven from the sun by the repulsion of See also:

• LIGHT

light and reach the earth's See also:

• ATMOSPHERE (Gr. fir µ6r, vapour; orkaipa, a sphere)

atmosphere, setting up See also:

• ELECTRICAL
• ELECTRICAL (or ELECTROSTATIC) MACHINE

electrical currents, See also:

• MANIFEST (Lat. manifestus, clear, open to view)

manifest in See also:

• AURORA
• AURORA (perhaps through a form ausosa from Sansk. ush, to burn ; the common idea of " brightness " suggests a connexion with aurum, gold)

aurora and magnetic disturbances .

Arrhenius's calculations, for the See also:

• SIZE

size of particle which he regarded as most probable, make the time of transmission to the earth slightly under two days . Amongst other theories which ascribe magnetic storms to See also:

• DIRECT

direct solar action may be mentioned that of Kr . Birkeland,49 who believes the vehicle to be See also:

• CATHODE

cathode rays . Ch . Nordmann60 similarly has suggested See also:

• RONTGEN, DAVID
• RONTGEN, WILHELM KONRAD (1845– )

Rontgen rays . Supposing the sun the ultimate source, it would be easier to discriminate between the theories if the exact time of the originating occurrence could be fixed . For instance, a disturbance that is propagated with the velocity of light may be due to Rontgen rays, but not to Arrhenius's particles . In support of his theory, Nordmann mentions several cases when conspicuous visual phenomena on the sun have synchronized with magnetic movements on the earth—the best known instance being the apparent coincidence in time of a magnetic disturbance at Kew on the 1st of See also:

• SEPTEMBER (Lat. septem, seven)

September 1859 with a remarkable solar outburst seen by R . C . See also:

• CARRINGTON, CHARLES

Carrington . Presumably any electrical phenomenon on the sun will set up waves in the See also:

• AETHER, or ETHER (Gr. deli p, probably from caeca, I burn, though Plato in his Cratylus (410 B)

aether, so transmission of electricand magnetic disturbances from the sun to the earth with the velocity .of light is a certainty rather than a, See also:

• HYPOTHESIS (from Gr. inrorcOivat, to put under; cf. Lat. suppositio, from sub-ponere)

hypothesis; but it by no means follows that the See also:

• ENERGY (from the Gr. ivipyela; iv, in, ipyov, work)

energy thus transmitted can give rise to sensible magnetic disturbances . Also, when considering Nordmann's coincidences, it must be remembered that magnetic movements are so numerous that it would be singular if no apparent coincidences had been noticed .

Another consideration is that the movements shown by See also:

• ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary magnetographs are seldom very rapid . During some. storms, especially those accompanied by unusually See also:

• BRIGHT, JOHN (1811-188g)
• BRIGHT, SIR CHARLES TILSTON

bright and rapidly varying auroral displays, large to and fro movements follow one another in See also:

• CLOSE
• CLOSE (from Lat. clausum, shut)
• CLOSE, MAXWELL HENRY (1822-1903)

close See also:

• SUCCESSION (Lat. successio, from succedere, to follow after)

succession, the changes being sometimes too See also:

• QUICK

quick to be registered distinctly on the photographic paper . This, however, is exceptional, even in polar regions where disturbances are largest and most numerous . As a See also:

• RULE

rule, even when the See also:

• CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change in the direction of movement in the declination See also:

• NEEDLE (O. Eng. ncedl; the word appears in various forms in Teutonic languages, Ger. Nadel, Dutch naal, the root being ne-, to sew, cf. Ger. nahen, and probably Lat. nere, to spin, Gr. vi)ats, spinning)

needle seems quite sudden, the movement in one direction usually lasts for several minutes, often for 1o, 15 or 30 minutes . Thus the cause to which magnetic disturbances are due seems in many cases to be persistent in one direction for a considerable time . § 38 . Attempts have been made to discriminate between the theories as to magnetic storms by a See also:

• CRITICAL (in alphabetical order of authors)

critical examination of the phenomena . A general connexion between sun-spot frequency and the See also:

• AMPLITUDE (from Lat. amplus, large)

amplitude of magnetic movements, See also:

• REGULAR

regular and irregular, is generally admitted . If it is a See also:

• CASE
• CASE, JOHN (d. 1600)

case of cause and effect, and the interval between the solar and terrestrial phenomena does not exceed a few hours, then there should be a sensible connexion between corresponding daily values of the sun-spot frequency and the magnetic range . Even if only some sun-spots are effective, we should expect when we select from a series of years two See also:

• GROUPS
• GROUPS, THEORY

groups of days, the one containing the days of most sun-spots, the other the days of least, that a prominent difference will exist between the mean values of the See also:

• ABSOLUTE (Lat. absolvere, to loose, set free)

absolute daily magnetic ranges for the two groups . Conversely, if we take out the days of small and the days of large magnetic range, or the days that are conspicuously quiet and those that are highly disturbed, we should expect a prominent difference between the corresponding mean sun-spot areas . An application of this principle was made by Chree43 to the five quiet days a See also:

• MONTH
• MONTH (a common Teutonic word, cf. Ger. Mond, Du. maand, Dan. maaned, &c., and cognate with Lat. mensis, Gr. µi7v, &c., in other branches of the Indo-Germanic family; all ultimately from the root seen in the word for the moon in nearly all those languages

month selected by the astronomer royal between 1890 and 1900 .

These days are very quiet relative to the See also:

• AVERAGE

average day and possess a much smaller absolute range . One would thus have expected on Birkeland's or Nordmann's theory the mean sun-spot frequency derived from Wolfer's provisional values for these days to be much below his mean value, 41.22, for the eleven years . It proved, however, to be 41.28 . This See also:

• PRACTICAL

practical identity was as visible in 1892 to 1895, the years of sun-spot maximum, as it was in the years of sun-spot minimum . Use was next made of the Greenwich projected sun-spot areas, which are the result of exact measurement . The days of each month were divided into three groups, the first and third—each normally of ten days—containing respectively the days of largest and the days of least sun-spot See also:

• AREA

area . The mean sun-spot area from See also:

• GROUP

group 1 was on the average about five times that for group 3 . It was then investigated how the astronomer royal's quiet days from 1890 to 1900, and how the most disturbed days of the period selected from the Kew24 magnetic records, distributed themselves among the three groups of days . Nineteen months were excluded, as containing more than ten days with no sun-spots . The remaining 113 months contained 565 quiet and 191 highly disturbed days, whose See also:

• DISTRIBUTION (Lat. distribuere, to deal out)

distribution was as follows: Group 1 . Group 2 . Group 3 .

Quiet days 179 195 191 Disturbed days 68 65 58 The group of days of largest sun-spot area thus contained slightly under their See also:

• SHARE (O. Eng. scearu, chiefly in compounds, e.g. land-scearu, a share of land, from sceran to cut; cf. " shear" )

share of quiet days and slightly over their share of disturbed days . The differences, however, are not large, and in three years, viz . 1895, 1897 and 1899, the largest number of disturbed days actually occurred in group 3, while in 1895, 1896 and 1899 there were fewer quiet days in group 3 than in group 1 . Taking the same distribution of days, the mean value of the absolute daily range of declination at Kew was calculated for the group 1 and the group 3 days of each month . The mean range from the group I days was the larger in 57% of the individual months as against 43 % in which it was the smaller . When the days of each month were divided into groups according to the absolute declination range at Kew, the mean sun-spot area for the group i days (those of largest range) exceeded that for the group 3 days (those of least range) in 55% of the individual months, as against 45% of cases in which it was the smaller . Taking next the five days of largest and the five days of least range in each month, sun-spot areas were got out not merely for these days themselves, but also for the next subsequent day and the four immediately preceding days in each case . On Arrhenius's theory we should expect the magnetic range to vary with the sun-spot area, not on the actual day but two days previously . The following figures give the percentage excess or deficiency of the mean sun-spot area for the respective groups of days, relative to the average value for the whole epoch dealt with. n denotes the day to which the magnetic range belongs, n+1 the day after, n—i the day before, and so on . Results are given for 1894 and 1895, the years which were on the whole the most favourable and the least favourable for Arrhenius's hypothesis, as well as for the whole eleven years . Day. n-4 n-3 n-2 n-I n n+I Five days of l 1894 +12 + 9 +11 +12 +11 +6 Five -16 -17 -15 -12 -II -10 95 largest range II yrs . + 9 + 8 + 8 + 7 + 5 +0.5 J( Five days of 1894 -I5j -17 -19 -2I -2I -19 least range II yrs. x-14 - 4 - 7' - 7 - 7 - 4 Taking the II-See also:

• YEAR

year-means we have the sun-spot area practically normal on the day subsequent to the representative day of large magnetic range, but sensibly above its mean on that day and still more so on the four previous days .

This suggests an emission from the sun taking a highly variable time to travel to the earth . The 11-year mean data for the five days of least range seem at first sight to point to the same conclusion, but the fact that the deficiency in sun-spot area is practically as prominent on the day after the representative day of small magnetic range as on that day itself, or the previous days, shows that the phenomenon is probably a secondary one . On the whole, taking into See also:

• ACCOUNT
• ACCOUNT (through O. Fr. acont, Late Lat. comptum, cornputare, to calculate)

account the extraordinary differences between the results from individual years, we seem unable to come to any very See also:

• POSITIVE (or PORTABLE) ORGAN

positive conclusion, except that in the See also:

• PRESENT

present See also:

• STATE
• STATE, GREAT OFFICERS OF

state of our knowledge little if any See also:

• CLUE

clue is afforded by the extent of the sun's spotted area on any particular day as to the magnetic conditions on the earth on that or any individual subsequent day . Possibly some more definite See also:

• INFORMATION (from Lat. informare, to give shape or form to, to represent, describe)

information might be extracted by considering the extent of spotted area on different zones of the sun . On theories such as those of Arrhenius or Maunder, effective See also:

• BOMBARDMENT

bombardment of the earth would be more or less confined to spotted areas in the zones nearest the centre of the visible hemisphere, whilst all spots on this hemisphere contribute to the total spotted area . Still the projected area of a spot rapidly diminishes as it approaches the edge of the visible hemisphere, i.e. as it recedes from the most effective position, so that the method employed above gives a preponderating See also:

• WEIGHT

weight to the central zones . One rather noteworthy feature in Table XL. is the tendency to a sequence in the figures in any one See also:

• ROW, JOHN (c. 1525—1580)

row . This seems to be due, at least in large See also:

• PART

part, to the fact that days of large and days of small sun-spot area tend to occur in groups . The same is true to a certain extent of days of large and days of small magnetic range, but it is unusual for the range to be much above the average for more than 3 or 4 successive days . § 39 . The records from ordinary magnetographs, even when run at the usual See also:

• RATE

rate and with normal sensitiveness, not infrequently show Pulsations. a repetition of regular or nearly regular small rhythmic movements, lasting sometimes for hours . The amplitude and period on different occasions both vary widely .

Periods of 2 to 4 minutes are the most See also:

• COMMON

common . W. van Bemmelen” has made a minute examination of these movements from several years' traces at Batavia, comparing the results with corresponding statistics sent him from Zi-ka-wei and Kew . Table XLI. shows the diurnal variation in the frequency of occurrence of these small movements—called pulsations by van Bemmelen—at these three stations . The Batavia results are from the years 1885 and 1892 to 1898 . Of the two sets of data for Zi-kawei (i) answers to the years 1897, 1898 and 1900, as given by van Bemmelen, while (ii) answers to the period 1900-1905, as given in the Zi-ka-wei Bulletin for 1905 . The Kew data are for 1897 . The results are expressed as percentages of the total for the 24 hours . There is a remarkable contrast between Batavia and Zi-ka-wei on the one See also:

• HAND
• HAND (a word common to Teutonic languages; cf. Ger. Hand, Goth. handus)
• HAND, FERDINAND GOTTHELF (1786-185r)

hand and Kew on the other, pulsations being much more numerous by See also:

• NIGHT

night than by day at the two former stations, whereas at Kew the exact See also:

• REVERSE

reverse holds . Van Bemmelen decided that almost all the occasions of pulsation at Zi-ka-wei were also occasions of pulsations at Batavia . The hours of commencement at the two places usually differed a little, occasionally by as much as 20 minutes; but this he ascribed to the fact that the earliest oscillations were too small at one or other of the stations to be visible on the trace . Remarkable coincidence between pulsations at Potsdam and in the See also:

• NORTH
• NORTH, BARONS
• NORTH, MARIANNE (1830—1890)
• NORTH, ROGER (1653-1734)
• NORTH, SIR THOMAS (1535?-16o1?)

north of See also:

• NORWAY
• NORWAY (Norge)

Norway has been noted by Kr . Birkeland.49 With magnetographs of greater sensitiveness and more open time scales, waves of shorter period be-come visible .

In 1882 F . Kohlrausch" detected waves with a period of about 12 seconds . Eschenhagen" observed a See also:

• GREAT

great variety of See also:

• SHORT, FRANCIS JOB (1857– )

short period waves, 30 seconds being amongst the most common . Some of the records he obtained suggest the superposition of regular sine waves of different periods . Employing a very sensitive See also:

• GALVANOMETER

galvanometer torecord changes of magnetic See also:

• INDUCTION (from Lat. inducere, to lead into; cf. Gr. ilrayu yli)

induction through a coil traversed by the earth's lines of force, H . See also:

• EBERT, FRIEDRICH ADOLF (1791-1834)

Ebert" has observed vibrations whose periods are but a small fraction of a second . 'Frye observations of Kohlrausch and Eschenhagen preceded the See also:

• RECENT

recent great development of applications of electrical See also:

• POWER [WILLIAM GRATTAN] TYRONE (1797-1841)

power, while longer period waves are shown in the Kew curves of 5o years ago, so that the existence of natural waves with periods of from a few seconds up to several minutes can hardly be doubted . Whether the much shorter period waves of Ebert are also natural is more open to doubt, as it is becoming exceedingly difficult in civilized countries to See also:

• ESCAPE (in mid. Eng. eschape or escape, from the O. Fr. eschapper, modern echapper, and escaper, low Lat. escapium, from ex, out of, and cappa, cape, cloak; cf. for the sense development the Gr. iichueoOat, literally to put off one's clothes, hence to sli

escape artificial disturbances . Hours . 0-3 . 3-6 . 6-9 .

9-Noon . I Noon-3 . 3-6 . 6-9 . ,9-I2 . Batavia 28 9 2 6 8 6 13 28 Zi-ka-wei(i) 33 5 2 7 4 4 10 35 „ (ii) 23 6 8 II 7 5 14 26 Kew . 4 8 19 14 22 18 See also:

• TII

tii 4 § 40 . The fact that the See also:

• MOON (a common Teutonic word, cf. Ger. Mond, Du. maan, Dan. maane, &c., and cognate with such Indo-Germanic forms as Gr. µlip, Sans. ma's, Irish mi, &c.; Lat. uses luna, i.e. lucna, the shining one, lucere, to shine, for the moon, but preserves the word i
• MOON, SIR RICHARD, 1ST BARONET (1814-1899)

moon exerts a small but sensible effect on the earth's magnetism seems to have been first discovered in 1841 by C . Kreil . Subsequently See also:

• SABINE, SIR EDWARD (1788-1883)

Sabine" investigated the nature of the lunar diurnal variation in declination Lunar at Kew, Toronto, See also:

• PEKIN

Pekin, St See also:

• HELENA
• HELENA, ST (c. 247-c. 327)

Helena, Cape of See also:

• GOOD, JOHN MASON (1764-1827)

Good See also:

• HOPE, ANTHONY
• HOPE, THOMAS (c. 1770-1831)

Hope Influence. and See also:

• HOBART
• HOBART, GARRET AUGUSTUS (1844–1899)
• HOBART, JOHN HENRY (1775-1830)

Hobart . The data in Table XLII. are mostly due to Sabine . They represent the mean lunar diurnal inequality in declination for the whole year .

The unit employed is o'•ooi, and as in our previous tables + denotes movement to the west . By " mean departure " is meant the See also:

• ARITHMETIC (Gr. apeOµ7run7, sc. TEXVn, the art of counting, from (ipLBµos, number)

arithmetic mean of the 24 hourly departures from the mean value for the lunar day; the range is the difference between the algebraically greatest and least of the hourly values . Not infrequently the mean departure gives the better See also:

• IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

idea of the importance of an inequality, especially when as in the present case two maxima and minima occur in the day . This See also:

• DOUBLE
• DOUBLE (from the Mid. Eng. duble, the form which gives the present pronunciation, through the Old Er. duble, from Lat. duplus, twice as much)

double daily period is unusually prominent in the case of the lunar diurnal inequality, and is seen in the other elements as well as in the declination . Lunar action has been specially studied in connexion with observations from See also:

• INDIA
• INDIA, FRENCH

India and See also:

• JAVA

Java . Broun55 at See also:

• TRIVANDRUM, or TREVANDRUM

Trivandrum and C . See also:

• CHAMBERS (the Fr. chambre, from Lat. camera, a room)
• CHAMBERS, EPHRAIM (d. 1740)
• CHAMBERS, GEORGE (1803-1840)
• CHAMBERS, ROBERT (18oz-1871)
• CHAMBERS, SIR WILLIAM (1726-1796)

Chambers 57 at Kolaba investigated lunar action from a variety of aspects . At Batavia van der See also:

• STOLE (Lat. stela and orarium, Fr. etole, It. stola, Sp. estola, Ger. Stela)

Stole" and more recently S . Figee 59 have carried out investigations involving an enormous amount of computation . Table XLIII. gives a See also:

• SUMMARY

summary of Figee's results for the mean lunar diurnal inequality at Batavia, for the two See also:

• HALF

half-yearly periods See also:

• APRIL

April to September (Winter or W.), and See also:

• OCTOBER

October to March (S.) . The + sign denotes movement to the west in the case of declination, but numerical increase in the case of the other elements . In the case of H and T (total force) the results for the two seasons present comparatively small differences, but in the case of D, I and V the amplitude and phase both differ widely .

Consequently a mean lunar diurnal variation derived from all the months of the year gives at Batavia, and presumably at other Lunar Kew . Toronto . Batavia . St Helena . Cape . Hobart . Hour . 1858-1862 . 1843-1848 . 1883-1899 . 1843-1847 . 1842-1846 .

1841-1848 . o +103 +315 -70 - 43 -148 - 98 + 160 +275 -63 - 5 -107 -138 2 +140 +158 -39 + 37 - 35 -142 3 + 33 + 2 - 8 + 70 + 43 -107 4 + lo -153 +38 + 85 +108 - 45 5 - 67 -265 +63 + 77 +140 + 27 6 -150 -302 +87 + 48 +132 + 88 7 -188 -255 +77 + 5 + 82 +122 8 -16o -137 +40 - 43 + 5 + 120 9 - 78 + 7 - 4 - 82 - 78 + 82 10 + 2 +178 -45 -102 -143 + 17 II + 92 +288 -8o - 98 -177 - 57 12 +160 +323 - 87 - 73 -165 -120 13 +188 +272 -68 - 32 -112 -152 14 +158 +148 -43 + 13 - 30 -147 15 + 90 - 17 - 8 + 52 + 58 -105 16 + to -18o +30 + 73 +132 - 35 17 - 85 -297 +62 + 73 +172 + 45 18 -142 -337 +72 + 52 +168 +112 19 -163 -290 +68 + 17 +122 +152 20 -147 -170 +52 - 25 + 45 +152 21 -123 - 7 + 8 - 58 - 40 +113 22 - 40 +155 -28 - 73 -112 + 47 23 + 27 +265 - 56 - 68 -153 - 30 Mean De- 105 200 50 54 104 93 parture Range . 376 66o 174 187 349 304 Declination Inclination,S . H . V . T . (unit o'•ooI) . (unit o'•ooI) . (unit 0.017) . (unit 0.017) . (unit 0.017) . Lunar W S .

W . S . W . S . W . S . W . S . Hour . o +30 -170 — I +25 -15 — 56 — 9 + 4 — 17 -47 1 +21 -147 -23 +49 -40 — 87 -54 +20 61 -67 ,- 2 + 5 — 83 -49 +69 -25 -107 -82 +37 - 62 -76 3 — 5 — 12 -51 +47 -21 — 76 -83 +24 — 59 -55 4 + I + 76 -37 +43 -13 — 59 -58 +18 — 39 -38 5 — 8 +134 -23 +12 +10 — 9 -27 +11 — 4 — 3 6 — 7 +181 — 2 -21 +21 + 43 + 9 — 6 + 23 +35 7 -10 +164 +30 -12 +23 + 45 +55 + 8 + 47 +43 8 — 7 + 86 +36 -21 +38 + 52 +71 — I + 68 +45 9 — 8 o +28 -23 +46 + 30 +64 -16 + 71 +19 10 — 5 — 85 +34 -20 +13 + 13 +54 -21 + 38 + 1 11 -15 -144 +27 —II —I2 — 6 +31 -19 + 5 -15 12 — 9 -164 +19 — 5 -47 -23 0 -19 -41 -29 13 +I -136 -3 +17 -59 -46 -36 -2 -69 -41 14 — 7 — 79 -13 +27 -66 — 44 -55 +14 — 84 -32 15 — 8 — 8 -32 +25 -53 — 37 -74 +14 — 82 -26 16 -12 + 72 -37 +25 -34 — 17 -70 +26 — 64 — 2 17 -13 +137 -33 + 4 — I + z8 -47 +21 — 24 +35 18 -2I +165 — 2 -10 +20 + 47 + 8 +12 + 21 +47 19 -12 +147 +21 -42 +44 + 81 +53 -14 + 64 +64 20 +10 + 95 +21 -62 +75 +107 +71 -28 +100 +80 21 +13 + 4 +26 -70 +65 + 98 +72 -44 + 92 +65 22 +25 — 82 +35 -41 +35 + 35 +68 -38 + 64 +12 23 +36 -147 +34 — 4 — 7 — 14 +44 -13 + 15 -19 Mean De- 12 150 26 29 33 48 50 18 51 37 parture Range 57 351 87 139 141 214 155 81 184 156 tropical stations, an inadequate idea of the importance of the lunar influence . In See also:

• JANUARY

January Figee finds for the range of the lunar diurnal inequality o.62 in D, 3.I7 in H and 3.5y in V, whereas the corresponding ranges in See also:

• JUNE

June are only 0'•13, I•Iy and 2.27 respectively . The difference between summer and winter is essentially due to solar action, thus the lunar influence on terrestrial magnetism is clearly a somewhat complex phenomepon .

From a study of Trivandrum data, Broun concluded that the action of the moon is largely dependent on the solar hour at the time, being on the average about twice as great for a day hour as for a night hour . Figee s investigations at Batavia point to a similar conclusion . Following a method suggested by Van der Stok, Figee arrives at a numerical estimate of the " lunar activity " for each hour of the solar day, expressed in terms of that at noon taken as See also:

• LOO (formerly called " Lanterloo," Fr. lanturlu, the refrain of a popular 17th-century song)

loo . In summer, for instance, in the case of D he finds the " activity " varying from 114 at to a.m. to only 8 at 9 p.m.; the corresponding extremes in the case of H are 139 at to a.m. and 54 at 6 a.m . The question whether lunar influence increases with sun-spot frequency is obviously of considerable theoretical See also:

• INTEREST

interest . See also:

• BALFOUR, FRANCIS MAITLAND (1851-1882)
• BALFOUR, ROBERT (known also as BALFOREUS) (1550?-1625?)
• BALFOUR, SIR JAMES (of Pittendreich) (d. 1583 Or 1584)
• BALFOUR, SIR JAMES, BART

Balfour See also:

• STEWART, ALEXANDER TURNEY (1803-1876)
• STEWART, BALFOUR (1828-1887)
• STEWART, CHARLES (1778–1869)
• STEWART, DUGALD (1753-1828)
• STEWART, J
• STEWART, JOHN (1749—1822)
• STEWART, JULIUS L
• STEWART, SIR DONALD MARTIN (1824–19o0)
• STEWART, SIR HERBERT (1843—1885)
• STEWART, SIR WILLIAM (c. 1540—c. 1605)
• STEWART, STUART
• STEWART, WILLIAM (c. 1480-c. 1550)

Stewart in the 9th edition of this See also:

• ENCYCLOPAEDIA

encyclopaedia gave some data indicating an appreciably enhanced lunar influence at Trivandrum during years of sun-spot maximum, but he hesitated to accept the result as finally proved . Figee recently investigated this point at Batavia, but with inconclusive results . Attempts have also been made to ascertain how lunar influence depends on the moon's declination and phase, and on her distance from the earth . The difficulty in these investigations is that we are dealing with a small effect, and a very See also:

• LONG, GEORGE (1800-1879)
• LONG, JOHN DAVIS (1838– )

long series of data would be required satisfactorily to eliminate other periodic influences . . § 41 . From an See also:

• ANALYSIS (Gr. avci and Meta, to break up into parts)

analysis of seventeen years data at St Petersburg and Pavlovsk, Leyst60 concluded that all the See also:

• PRINCIPAL

principal See also:

• PLANETS, MINOR

planets Planetary sensibly influence the earth's magnetism . According to influence. his figures, all the planets except See also:

• MERCURY
• MERCURY (MERCU1uus)
• MERCURY (symbol Hg, atomic weight = 2oo)

Mercury—whose in- fluence he found opposite to that of the others—when nearest the earth tended to deflect the declination magnet at St Petersburg to the west, and also increased the range of the diurnal inequality of declination, the latter effect being the more conspicuous .

Schuster,61 who has considered the evidence advanced by Leyst from the mathematical standpoint, considers it to be inconclusive . § 42 . The best way of carrying out a magnetic survey depends on where it has to be made and on the See also:

• OBJECT

object in view . The object that Magnetic probably still comes first in importance is a knowledge Surveys. of the declination, of sufficient accuracy for See also:

• NAVIGATION (from Lat. navis, ship, and agere, to move)

navigation in. all navigable See also:

• WATERS, TERRITORIAL

waters . One might thus infer that magnetic surveys consist mainly of observations at See also:

• SEA (in O. Eng. sae, a common Teutonic word; cf. Ger. See, Dutch Zee, &c.; the ultimate source is uncertain)
• SEA, COMMAND OF THE

sea . This cannot however be said to be true of the past, whatever it may be of the future, and this for several reasons . Observations at sea See also:

• ENTAIL (from Fr. tailler, to cut; the old derivation from tales haeredes is now abandoned)

entail the use of a See also:

• SHIP

ship, specially constructed so as to be See also:

• FREE

free fromdisturbing influence, and so are inherently costly; they are also See also:

• APT

apt to be of inferior accuracy . It might be possible in quiet See also:

• WEATHER (O. Eng. weder; the word is common to Teutonic languages; cf. Du. weder, Dan. veir, Icel. ve8r, and Ger. Wetter and Gewitter, storm; the root is wa- to blow, from which is derived " wind ")

weather, in a large See also:

• VESSEL (O. Fr. vaissel, from a rare Lat. vascellum, dim. of vas, vase, urn)

vessel free from vibration, to observe with See also:

• INSTRUMENTS

instruments of the highest precision such as a unifilar magneto-See also:

• METER, ELECTRIC

meter, but in the ordinary See also:

• SURVEYING

surveying ship apparatus of less sensitiveness has to be employed . The declination is usually determined with some See also:

• FORM (Lat. forma)

form of See also:

• COMPASS (Fr. corn pas, ultimately from Lat. cum, with, and passus, step)

compass . The other elements most usually found directly at sea are the inclination and the total force, the See also:

• INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

instrument employed being a special form of See also:

• INCLINOMETER (Dip CIRCLE)

inclinometer, such as the See also:

• FOX
• FOX, C
• FOX, CHARLES JAMES (1749-1806)
• FOX, EDWARD (c. 1496-1538)
• FOX, GEORGE (1624-1691)
• FOX, RICHARD (c. 1448-1528)
• FOX, ROBERT WERE (1789—1877)
• FOX, SIR STEPHEN (1627–1716)
• FOX, SIR WILLIAM (1812-1893)

Fox circle, which was largely used by See also:

• ROSS
• ROSS, ALEXANDER (1699-1784)
• ROSS, GEORGE WILLIAM (1841- )
• ROSS, JOHN, or KOOESKOOWE (179o-1866)
• ROSS, ROBERT (1766-1814)
• ROSS, SIR HEW DALRYMPLE (1779-1868)
• ROSS, SIR JAMES CLARK (1800-1862)
• ROSS, SIR JOHN (1777-1856)

Ross in the See also:

• ANTARCTIC
• ANTARCTIC (Gr. &vri, opposite, and apKTos, the Bear, the northern constellation of Ursa Major)

Antarctic, or in recent years the See also:

• LLOYD, EDWARD (1845— )
• LLOYD, WILLIAM (1627–1717)
• LLOYD, WILLIAM WATKISS (1813–1893)

Lloyd-Creak . This latter instrument differs from the ordinary See also:

• DIP (Old Eng. dyppan, connected with the common Teutonic root seen in " deep ")

dip-circle fitted for total force observations after H . Lloyd's method mainly in that the needles See also:

• REST (O. Eng. rest, reste, bed, cognate with other Teutonic forms, e.g. Ger. Rast, Riiste, rest, and probably Gothic Rasta, league, i.e. resting or stopping place)

rest in pivots instead of on See also:

• AGATE

agate edges .

To overcome See also:

• FRICTION (from Lat. fricare, to rub)

friction a projecting See also:

• PIN (a doublet with " pen " from Lat. pinna, feather, pinnacle, which is said to contain the same root as irirvs, pine tree, and properly to mean a sharp point or end)

pin on the framework is scratched with a roughened See also:

• IVORY (Fr. ivoire, Lat. ebur)
• IVORY, SIR JAMES (1765-1842)

ivory See also:

• PLATE

plate . The most notable recent example of observations at sea is afforded by the cruises of the surveying See also:

• SHIPS

ships " See also:

• GALILEE
• GALILEE (Heb. 5'S?, " border " or " ring," Gr. I'aXi?aia)
• GALILEE, SEA OF

Galilee " and " See also:

• CARNEGIE
• CARNEGIE, ANDREW (1837– )

Carnegie " under the auspices of the Carnegie Institution of See also:

• WASHINGTON
• WASHINGTON (or WASHINGTON COURT HOUSE)
• WASHINGTON, BOOKER TALIAFERRO (c. 1859– )
• WASHINGTON, BUSHROD (1762-1829)
• WASHINGTON, GEORGE (1732-1799)

Washington, which includes in its magnetic See also:

• PROGRAMME, or PROGRAM

programme a general survey . To see where the ordinary See also:

• LAND

land survey assists navigation, let us take the case of a See also:

• COUNTRY (from the Mid. Eng. contre or contrie, and O. Fr. cuntree; Late Lat. contrata, showing the derivation from contra, opposite, over against, thus the tract of land which fronts the sight, cf. Ger. Gegend, neighbourhood)

country with a long sea-See also:

• BOARD (O. Eng. bord)

board . If observations were taken every few See also:

• MILES, NELSON APPLETON (1839— )

miles along the See also:

• COAST (from Lat. costa, a rib, side)

coast results might be obtained adequate for the ordinary wants of See also:

• COASTING

coasting steamers, but it would be difficult to infer what the declination would be 50 or even 20 miles off See also:

• SHORE

shore at any particular place . If, however, the land area itself is carefully surveyed, one knows the trend of the lines of equal declination, and can usually extend them with considerable accuracy many miles out to sea . One also can tell what places if any on the coast suffer from See also:

• LOCAL

local disturb- ances, and thus decide on the See also:

• NECESSITY (Lat. necessitas)

necessity of special observations . This is by no means the only immediately useful purpose which is or may be served by magnetic surveys on land . In Scandinavia use has been made of magnetic observations in prospecting for See also:

• IRON [symbol Fe, atomic weight 55.85 (0=16)]

iron ore . There are also various See also:

• GEOLOGICAL

geological and See also:

• GEODETIC

geodetic problems to whose See also:

• SOLUTION (from Lat. solvere, to loosen, dissolve)

solution magnetic surveys may afford valuable guidance . Among the most important recent surveys may be mentioned those of the See also:

• BRITISH

British Isles by A . Rucker and T . E .

Thorppe,6E of See also:

• FRANCE
• FRANCE, ANATOLE (1844– )

France and See also:

• ALGERIA
• ALGERIA (Algerie)

Algeria by Moureaux68 of See also:

• ITALY
• ITALY (Italia)

Italy by Chistoni and Palazzo,64 of the See also:

• NETHERLANDS

Netherlands by Van Ryckevorsel,65 of See also:

• SOUTH
• SOUTH, ROBERT (1634–1716)

South See also:

• SWEDEN
• SWEDEN [Sverige]
• SWEDEN, NORWAY AND

Sweden by Carlheim Gyllenskiold,66 of See also:

• AUSTRIA
• AUSTRIA, LOWER (Ger. Niederosterreich or Osterreich unter der Enns, " Austria below the river Enns ")
• AUSTRIA, UPPER (Ger. Oberosterreich or Osterreich ob der Enns, " Austria above the river Enns ")

Austria-See also:

• HUNGARY
• HUNGARY (Hungarian Magyarorszdg)

Hungary by Liznar,87 of See also:

• JAPAN

Japan by Tanakadate,88 of the East Indies by Van Bemmelen, and South See also:

• AFRICA
• AFRICA, ROMAN

Africa by J . C . See also:

• BEATTIE, JAMES (1735—1803)

Beattie . A survey of the See also:

• UNITED

United States has been proceeding for a good many years, and many results have appeared in the publications of the U.S . Coast and Geodetic Survey, especially See also:

• BAUER, BRUNO (1809-1882)

Bauer's Magnetic Tables and Magnetic Charts, 1908 . Additions to our knowledge may also be expected from surveys of India, See also:

• EGYPT

Egypt and New See also:

• ZEALAND (also SEALAND Or SEELAND; Danish Sjaelland)

Zealand . For the satisfactory See also:

• EXECUTION (from Lat. ex-sequor, exsecutus, follow or carry out)

execution of a land survey, the observers must have absolute instruments such as the unifilar See also:

• MAGNETOMETER

magnetometer and dip circle, suitable for the accurate determination of the magnetic elements, and they must be able to See also:

• FIX, THEODORE (180o-1846)

fix the exact positions of the spots where observations are taken . If, as usual, the survey occupies several years, what is wanted is the value of the elements not at the actual time of observation, but at some fixed epoch, possibly some years earlier or later . At a magnetic See also:

• OBSERVATORY

observatory, with standardized records, the difference between the values of a magnetic element at any two specified instants can be derived from the magnetic curves . But at an ordinary survey station, at a distance from an observatory, the information is not immediately available . Ordinarily the reduction to a fixed epoch is done in at least two stages, a correction being applied for See also:

• SECULAR (Lat. saecularis, of or belonging to an age or generation, saeculum)

secular change, and a second for the departure from the mean value for the day due to the regular diurnal inequality and to disturbance . The reduction to a fixed epoch is at once more easy and more accurate if the area surveyed contains, or has close to its See also:

• BORDERS, THE

borders, a well distributed series of magnetic observatories, whose records are See also:

• CORN (a common Teutonic word; cf. Lat. granum, seed, grain)
• CORN (fromm Lat. corms, horn)

corn, See also:

• PARABLE (Gr. 7apa(3oXi7, a comparison or similitude)

parable and trustworthy .

Throughout an area of the size of France or See also:

• GERMANY
• GERMANY (Ger. Deutschland)

Germany, the secular change between any two specified See also:

• DATES

dates can ordinarily be expressed with sufficient accuracy by a See also:

• FORMULA
• FORMULA (Lat. diminutive of forma, shape, pattern, &c., especially used of rules of judicial procedure)

formula of the type S=do+a(l—lo)+b(X—Xo) . . (i), where E denotes secular change, l See also:

• LATITUDE (Lat. latitudo, latus, broad)

latitude and a See also:

• LONGITUDE (from Lat. longitudo, " length ")

longitude, the letters with suffix o See also:

• RELATING

relating to some convenient central position . The constants So, a, b are to be determined from the observed secular changes at the fixed observatories whose See also:

• GEOGRAPHICAL

geographical co-ordinates are accurately known . Unfortunately, as a rule, fixed observatories are few in number and not well distributed for survey purposes; thus the secular change over part at least of the area has usually to be found by repeating the observations after some years at several of the See also:

• FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
• FIELD, CYRUS WEST (1819-1892)
• FIELD, DAVID DUDLEY (18o5-1894)
• FIELD, EUGENE (1850-1895)
• FIELD, FREDERICK (18o1—1885)
• FIELD, HENRY MARTYN (1822-1907)
• FIELD, JOHN (1782—1837)
• FIELD, MARSHALL (183 1906)
• FIELD, NATHAN (1587—1633)
• FIELD, STEPHEN JOHNSON (1816-1899)
• FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)

field stations . The success attending this depends on the exactitude with which the sites can be recovered, on the accuracy of the observations, and on the success with which See also:

• ALLOWANCE (from "allow,' derived through 0. Fr. alouer from the two Lat. origins adlaudare, to praise, and allocare, to assign a place; so that the English word combined the general idea of "assigning with approval")

allowance is made for diurnal changes, regular and irregular . I t is thus desirable that the observations at repeat stations should be taken at hours when the regular diurnal changes are slow, and that they should not be accepted unless taken on days that prove to be magnetically quiet . Unless the secular change is exceptionally rapid, it will usually be most convenient in practice to calculate it from or to the See also:

• MIDDLE

middle of the month, and then to allow for the difference between the mean value for the month and the value at the actual hour of observation . There is here a difficulty, inasmuch as the latter part of the correction depends on the diurnal inequality, and so on the local tirne of the station . No altogether satisfactory method of surmounting this difficulty has yet been proposed . Rucker and See also:

• THORPE [or TnoRP], JOHN (/l. 1570-1618)
• THORPE, BENJAMIN (1782-1870)

Thorpe in their British survey assumed that the divergence from the mean value at any hour at any station might be regarded as made up of a regular diurnal inequality, identical with that at Kew when both were referred to local time, and of a disturbance element identical with that existing at the same absolute time at Kew . Suppose, for instance, that at hour h G.M.T. the departure at Kew from the mean value for the month is d, then the corresponding departure from the mean at a station X degrees west of Kew is d—e, where e is the in-crease in the element at Kew due to the regular diurnal inequality between hour h—a/15 and hour h . This See also:

• PROCEDURE (Fr. procedure, from Lat. procedere, to go for-ward)

procedure is See also:

• SIMPLE

simple, but is exposed to various criticisms .

If we define a diurnal inequality as the result obtained by combining hourly readings from all the days of a month, we can assign a definite meaning to the diurnal inequality for a particular month of a particular year, and after the curves have been measured we can give exact numerical figures answering to this See also:

• DEFINITION (Lat. definitio, from de-finire, to set limits to, describe)

definition . But the diurnal inequality thus obtained differs, as has been pointed out, from that derived from a limited number of the quietest days of the month, not merely in amplitude but in phase, and the view that the diurnal changes on any individual day can be regarded as made up of a regular diurnal inequality of definite See also:

• CHARACTER (Gr. xapareri7p, from xap&crew, to scratch)

character and of a disturbance element is an hypothesis which is likely at times to be considerably wide of the See also:

• MARK
• MARK, CARL (1858– )
• MARK, GOSPEL OF ST
• MARK, ST

mark . The extent of the See also:

• ERROR (Lat. error, from errare, to wander, to err)

error involved in assuming the regular diurnal inequality the same in the north of See also:

• SCOTLAND
• SCOTLAND, CHURCH OF
• SCOTLAND, EPISCOPAL CHURCH OF

Scotland, or the west of See also:

• IRELAND
• IRELAND, CHURCH
• IRELAND, CHURCH OF
• IRELAND, JOHN (1761-1842)
• IRELAND, JOHN (1838- )
• IRELAND, WILLIAM HENRY (1777-1835)

Ireland, as in the south-east of See also:

• ENGLAND
• ENGLAND, THE CHURCH OF

England remains to be ascertained . As to the disturbance element, even if the disturbing force were of given magnitude and direction all over the British Isles—which we now know is often very far from the case—its effects would necessarily vary very sensibly owing to the considerable variation in the direction and intensity of the local undisturbed force . If observations were confined to hours at which the regular diurnal changes are slow, and only those taken on days of little or no disturbance were utilized, corrections combining the effects of regular and irregular diurnal changes could be derived from the records of fixed observations, supposed suitably situated, combined in formulae of the same type as (i) . § 43 . The field results having been reduced to a fixed epoch, it remains to combine them in ways likely to be useful . In most cases the results are embodied in charts, usually of at least two kinds, one set showing only general features, the other the See also:

• CHIEF (from Fr. chef, head, Lat. caput)

chief local peculiarities . Charts of the first See also:

• KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind resemble the See also:

• WORLD

world charts (See also:

• FIGS

figs. i to 4) in being free from See also:

• SHARP, GRANVILLE (1735-1813)
• SHARP, JAMES (1618-1679)
• SHARP, JOHN (1645-1714)
• SHARP, RICHARD (1759-1835)
• SHARP, WILLIAM (1749-1824)
• SHARP, WILLIAM (1856-1905)

sharp twistings and convolutions . In these the declination for instance at a fixed geographical position on a particular isogonal is to be regarded as really a mean from a considerable surrounding area . Various ways have been utilized for arriving at these terrestrial isomagnetics—as Rucker and Thorpe See also:

• CALL (from Anglo-Saxon ceallian, a common Teutonic word, cf. Dutch kallen, to talk or chatter)

call them—of which an elaborate discussion has been made by E . Mathias.° From a theoretical standpoint the simplest method is perhaps that employed by Liznar for Austria-Hungary .

Let 1 and a represent latitude and longitude relative to a certain central station in the area . Then assume that throughout the area the value E of any particular magnetic element is given by a formula E = Eo+al+bX+cL +dX2+elX, where Eo, a, br c, d, e are absolute constants to be determined from the observations . When determining the constants, we write for E in the See also:

• EQUATION (from Lat. aequatio, aequare, to equalize)

equation the observed value of the element (corrected for secular change, &c.) at each station, and for l and X the latitude and longitude of the station relative to the central station . Thus each station contributes an equation to assist in determining the six constants . They can thus be found by least squares or some simpler method . In Liznar's case there were 195 stations, so that the labour of applying least squares would be considerable . This is one objection to the method . A second is that it may allow undesirably large weight to a few highly disturbed stations . In the case of the British Isles, Rucker and Thorpe employed a different method . The area was split up into districts . For each See also:

• DISTRICT

district a mean was formed of the observed values of each element, and the mean was assigned to an imaginary central station, whose geographical co-ordinates represented the mean of the geographical co-ordinates of the actual stations . Want of uniformity In the distribution of the stations may be allowed for by weighting the results .

Supposing Eo the value of the element found for the central station of a district, it was assumed that the value E at any actual station whose latitude and longitude exceeded those of the central station by 1 and a was given by E = Eo+al+bX, with a and b constants throughout the district . Having found Eo, a and b, Rucker and Thorpe calculated values of the element for points defined by whole degrees of longitude (from Greenwich) and half degrees of latitude . Near the common border of two districts there would be two calculated values, of which the arithmetic mean was accepted . The next step was to determine by See also:

• INTERPOLATION (from Lat. interpolare, to alter, or insert something fresh, connected with pollee, a polish)

interpolation where isogonals —or other isomagnetic lines—cut successive lines of latitude . The curves formed by joining these successive points of intersection were called district lines or curves . Rucker and Thorpe's next step was to obtain formulae by trial, giving smooth curves of continuous curvature—terrestrial isomagnetics—approximating as closely as possible to the district lines . The curves thus obtained had somewhat complicated formulae . For instance, the isogonals south of 54°.5 latitude were given for the epoch See also:

• JAN

Jan . 1, 1891 by D=18° 37'-1-18'•5(1—49.5)—3'•5 See also:

• COS
• COS, or STANKO (Ital. Stanchio, Turk. Islan-keui, by corruption from Etc rav KW)

cos 145°(1—49.5)} +126'.3+1'•5(1—49'5)1(X—4)+0'•01(X—4)2(1—54'5)2, where D denotes the See also:

• WESTERLY