LOG (a word of uncertain etymological origin,possibly onomatopoeic; the New

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• ENGLISH

English

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• DICTIONARY

Dictionary rejects the derivation from

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• NORWEGIAN

Norwegian lag, a fallen

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• TREE (0. Eng. treo, treow, cf. Dan. tree, Swed. Odd, tree, trd, timber; allied forms are found in Russ. drevo, Gr. opus, oak, and 36pv, spear, Welsh derw, Irish darog, oak, and Skr. dare, wood)
• TREE, SIR HERBERT BEERBOHM (1853- )

tree)  , a large piece of, generally unhewn, wood . The word is also used in various 'figurative senses, and more particularly for the " nautical log," an apparatus for ascertaining the speed of ships . Its employment in this sense depends on the fact that a piece of wood attached to a line was thrown overboard to lie like a log in a fixed position, motionless, the vessel's speed being calculated by observing what length of line ran out in a given time (" common log ") ; and the word has been retained for the modern " patent " or " continuous " log, though it works in an entirely different manner . The origin of the " common log " is obscure, but the beginnings of the " continuous log " may be traced back to the 16th century . By an invention probably due to Humfray Cole and published in 1578 by William Bourne in his Inventions and Devices, it was proposed to register a ship's .speed by means of a " little small close boat," with a wheel, or wheels, and an axle-tree to turn clockwork in the little boat, with dials and pointers indicating fathoms, leagues, scores of leagues and hundreds of leagues . About 1668 Dr R . Hooke showed some members of the Royal Society an instrument for the same purpose, depending on a vane or fly which rotated as the vessel progressed (Birch, History of the Royal Society, iv . 231), and Sir Isaac Newton in 1715 reported unfavourably on the " marine surveyor " of Henry de Saumarez, which also depended on a rotator . Conradus Mel in his Antiquarius Sacer (1719) described a " pantometron nauticum " which he claimed would show without calculation the distance sailed by the ship; and J . Smeaton in 1754 published improvements on the apparatus of Saumarez . William Foxon of Deptford in 1772, James Guerimand of Middlesex in 1776 (by his " marine perambulator "), and R . H .

Gower in 1772, practically demonstrated the registration of a vessel's speed z in. thick, with a radius of 5 or 6 in., the circumference of which is weighted with lead to keep it upright and retard its passage through the water . Two holes are made near its lower angles . One end of a short piece of thin line is passed through one of these holes, and knotted; the other end has spliced to it a hard bone peg which is inserted in the other hole . The holes are so placed that the log-ship will hang square from the span thus formed . The log-line is secured to this span and consists of two parts . The portion nearest the log-ship is known as the "'stray line "; its length varies from to to 20 fathoms, but should be sufficient to ensure that the log-ship shall be outside the dis- turbing element of the ship's wake . The point where it joins the other part is marked by a piece of bunting, and the line from this point towards its other end is marked at known intervals with " knots," which consist of pieces of cord worked in between its strands . A mean degree of the meridian being assumed to be 69.0q statute miles of 528o ft., the nautical mile (4 degree) is taken as 6o8o ft., which is a sufficiently close approximation for practical purposes, and the distances between the knots are made to bear the same relation to 6o8o ft. as 28 seconds to an hour (3600 seconds) ; that is, they are placed at intervals of 47 ft . 3 in . The end of the first interval of this length (counting from the piece of bunting) is marked by a bit of leather, the second by a cord with two knots, the third by one with three knots, and so on; the middle of each of these lengths (half-knot) is also marked by a cord with one knot . It follows that, if, say, five knots of the line run out in 28 seconds, the ship has gone 5X471 ft. in that time, or is moving at the rate of 5 X 6o8o ft . (=five nautical miles) an hour; hence the common use of knot as equivalent to a nautical mile .

In the log-

glass the time is measured by running sand, which, however, is apt to be affected by the humidity of the atmosphere . Sometimes a 3o-second glass is used instead of a 28-second one, and the intervals between the knots on the log-line are then made 50 ft . 7 in, instead of 47 ft . 3 in . For speeds over six knots a 14-second glass is employed, and the speed indicated by the log-line is doubled . The log-line, after being well soaked, stretched and marked with knots, is wound uniformly on the log-reel, to which its inner end is securely fastened . To " heave the log," a man holds the log-reel over his head (at high speeds the man and portable reel are superseded by a fixed reel and a winch fitted with a brake), and the officer places the peg in the log-ship, which he then throws clear and to windward of the ship, allowing the line to run freely out . When the bunting at the end of the stray line passes his hand, he calls to his assistant to turn the glass, and allows the line to pay out freely . When all the sand has run through, the assistant calls " Stop ! " when the log-line is quickly nipped, the knots counted, and the inter-mediate portion estimated . The strain on the log-ship when the log-line is nipped, causes the peg to be withdrawn from it, and the log-ship is readily hauled in . In normal circumstances the log is hove every hour .

In a

steam vessel running at high speed on an ocean route, with engines working smoothly and uniformly, a careful officer with correct line and glass can obtain very accurate results with the common log . Ground Log.—In the deltas of shoal rivers, with a strong tide or current and no land visible, a 5 lb lead is substituted for the log-ship; the lead rests on the bottom, and the speed is obtained in a manner similar to that previously described . Such a " ground-log " indicates the actual speed over the ground, and in addition, when the log-line is being hauled in, it will show the real course the ship is making over the ground . Patent Log.—The screw or rotatory log of Edward Massey, invented in 1802, came into gen'ral use in 1836 and continued until 1861 . The re- gistering wheel-work was contained in a shallow rectangular box (fig . 2); with a FIG . 2 . float plate on its upper side, carrying three indicating dials, recording respectively fractions, units and tens of miles (up to a hundred) . The rotator was connected to the log by a rope 6 ft. in length, actuating a universal joint on the first spindle of the register; it consisted of an air-tight thin metal tube with a coned fore-end, carrying flat metal vanes set at an angle . Alexander Bain in 1846 suggested enclosing the wheelwork in the rotator . In Thomas Walker's harpoon or frictionless log, introduced in 1861, the wheelwork was enclosed in a cylindrical case of the same diameter as the body of the rotator or fan, and the latter was brought close up to the register, forming a com- pact machine and avoid- ing the use of the 6-ft. line . Two years later a heart-shaped float plate was attached to the case; and the log called the Al Harpoon ship log (fig .

3) . The log should be washed in fresh water when practicable, to prevent oxidization of the wheels, and be lubricated with suitable oil through a hole in the case . These logs were towed from the ship, but with

quick passages and well surveyed coasts, the need arose for a patent log which could be readily consulted from the deck, and from which the distance run under varying speeds could be quickly ascertained . To meet this requirement, Walker in 1878 introduced the Cherub by mechanical means . Viscount de Vaux in 18o7 made use of water-pressure, as did the Rev . E . L . Berthon in 1849, and C . E . Kelway invented an electrical log in 1876 . Common Log.—To ascertain the ship's speed by the common log four articles are necessary—a log-ship or log-chip, log-reel, log-line and log-glass . The log-ship (fig .

1) is a wooden quadrant log (fig . 4), a taffrail one, which, however, is not as a

rule used for register on the taffrail to be recorded in the chart room or any other speeds over r8 knots . Owing to the increased friction produced part of the vessel as desired, a chart room electric register has been introduced . By means of an electric installation between the log by a rotator making approximately 90o revolutions per mile, register aft and the electric register in the chart room, every tenth of towed at the end of a line varying from 4o fathoms for a 12-knot a mile indicated by the former is recorded by the latter . Walker's Rocket log (fig. to) is a taffrail one, with bearings of hardened steel, and is intended to be slung or secured. tb the taffrail by aline; the mbar pat-tern has a fitting for the deck . In taff rail logs, the movement of the line owing to its length becomes spasmodic and jerky, increasing the vibration and friction; to ob- viate this a governor or fly-wheel is introduced, the hook of the tow line K (fig . II) and the eye of the register M being attached to the governor . Fig . 11 represents the arrangement fitted to the Neptune log ; with the Cherub log, a small piece of line is in- troduced between the FIG . 7.—Dial-plate of Neptune Log. governor and the eye of- the register . The two principal American taff rail logs are the Negus and Bliss (Messrs Norie and Wilson) . The former bears a general resemblance to the Cherub" log, but the dial plate is horizontal and the faces turn upwards .

The

main shaft bearings are in two sets and composed of steel balls running in steel cones and cups; the governor is an iron rod about 16 in. long, with I in. balls at the extremities . The Bliss resembles the Rocket log in shape, and is secured to the taffrail by a rope or slung . A governor is not employed . The blades of the rotator are adjustable, being fitted into its tube or body by slits and holes and then soldered . The outer ends of the blades are slit (fig . 12) to form two tongues, and with the wrench (fig . 12) the angle of the pitch can be altered . All patent logs have errors, the amounts of which should be ascertained by shore observations when passing a well surveyed coast in tideless waters on a calm day . Constant use, increased friction (more especially at high speeds), and damage to the rotator will alter an ascertained log error; head or following seas, strong winds, currents and tidal streams also affect the correctness . FIG . 8.—Ball Bearings of Neptune Log . A Log Book is a marine or sea journal; containing, in the British navy, the speed, course, leeway, direction and force of the wind, state of the weather, and barometric and thermometric observations .

Under the heading " Remarks " are noted (for K vessels with

sail power) making, shorten- ing and trimming sails; and (for all G' ships) employment of crew, times of passing prominent landmarks, altering of course, and any subject of interest and in Skeleton Case . FIG . Io.—Rocket Log . importance . The deck log book, kept by the officers of the watch, is copied into the ship's log book by the navigating II Rotator . F speed to 6o fathoms for 20 knots, the pull of the line and rotator is borne by coned rollers, having• their outlines tapering to a common point in their rotation, thus giving a broad rolling surface . Strong worms and wheels are substituted for the light clockwork . In fig . 4 the shoe H is secured to the taffrail, and the rotator in the water is hooked to the eye of the spindle M by the hook D . The case A contains the registering wheelwork and a sounding bell . The half gimbal B pivoting in the socket of the base C allows the register to receive the strain in the direct line . The bearings and rollers are lubricated with castor oil every twelve hours through holes in the sliding case E, and can be examined by unscrewing the case E and the eye M .

When not in use, the register is removed from the shoe by lifting a small screw

button near C . The tow line is usually plaited, and to avoid a knot close to the rotator, the latter is secured to the former by a knot inside an egg-shaped shell (fig . 5, Neptune pattern) . Walker's Neptune log (fig . 6) is used for vessels of high speed . Case A contains the wheelwork, and case E the spindle and steel ball bearings; in each case are openings, closed by sliding tubes, for examination and lubrication . In fig . 6 the cases A and E are shown open . Fig . 7 shows the dial plate . In fig . 8 the ball bearings are shown unscrewed from the body of the log, with eye, cap and spindle .

They consist of two rows of balls rolling in two pairs of V races or grooves . The outer pair receive the strain of the rotator, and the inner are for

adjustment and to prevent lateral movement . The balls and races are enclosed in a skeleton cage (fig . 9) unscrewing from the cap F (fig . 6) for cleaning or renewal; the adjustment of the bearings is made by screwing up the cage cap b, locked by a special washer and the two screws a, a (figs . 8, 9) . If the outer races become worn, the complete cage and bearings are reversed; the strain of the line is then transferred to what had previously been the inner with practically unworn balls and races . It is for this purpose that the skeleton cage is screwed internally at both ends, fitting a screwed ring inside the cap F (fig . 6) . To enable the indications of the log officer, and the latter is an official journal . In steam vessels a rough and fair engine room register are kept, giving information with regard to the engines and boilers . In the British mercantile marine all ships (except those employed exclusively in trading between ports on the coasts of Scotland) are compelled to keep an official log book in a form approved by the Board of Trade .

A

mate's log book and engine room register are not compulsory, but are usually kept .