See also:English physicist, was
See also:born on the 24th of
See also:December 1818, at
See also:Salford, near Manchester . Although he received some instruction from
See also:John Dalton in chemistry, most of his scientific knowledge was self-taught, and this was especially the case with regard to
See also:electricity and electro-magnetism, the subjects in which his earliest researches were carried out . From the first he appreciated the importance of accurate measurement, and all through his
See also:life the attainment of exact quantitative data was one of his chief considerations . At the age of nineteen he invented an electromagnetic engine, and in the course of examining its performance dissatisfaction with vague and arbitrary methods of specifying electrical quantities caused him to adopt a convenient and scientific unit, which he took to be the amount of electricity required to decompose nine grains of
See also:water in one
See also:hour . In 184o he was thus enabled to give a quantitative statement of the
See also:law according to which
See also:heat is produced in a conductor by the passage of an electric current, and in succeeding years he published a series of valuable researches on the agency of electricity in transformations of energy . One of these contained the first intimation of the achievement with which his name is most widely associated, for it was in a paper read before the
See also:British Association at
See also:Cork in 1843, and entitled " The Calorific Effects of Magneto-electricity and the
See also:Mechanical Value of Heat," that he expressed the conviction that whenever mechanical force is expended an exact
See also:equivalent of heat is always obtained . By rotating a small electro-magnet in water, between the poles of another magnet, and then measuring the heat
See also:developed in the water and other parts of the machine, the current induced in the coils, and the energy required to maintain rotation, he calculated that the quantity of heat capable of warming one pound of water one degree F. was equivalent to the mechanical force which could raise 838 lb. through the distance of one
See also:foot . At the same
See also:time he brought forward another determination based on the
See also:heating effects observable when water is forced through capillary tubes; the number obtained in this way was 770 . A third method, depending on the observation of the heat evolved by the mechanical
See also:compression of air, was employed a
See also:year or two later, and yielded the number 798; and a fourth—the well-known frictional one of stirring water with a sort of paddlewheel—yielded the result 890 (see Brit . Assoc .
See also:Report, 1845), though 781.5 was obtained by subsequent repetitions of the experiment . In 1849 he presented to the Royal Society a memoir which, together with a
See also:history of the subject, contained details of a long series of determinations, the result of which was 772 .
See also:good many years later he was entrusted by the
See also:committee of the British Association on
See also:standards of electric resistance with the task of deducing the mechanical equivalent of heat from the thermal effects of electric currents . This inquiry yielded (in 1867) the result 783, and this
See also:Joule himself was inclined to regard as more accurate than his old determination by the frictional method; the latter, however, was repeated with every precaution, and again indicated 772.55 foot-pounds as the quantity of
See also:work that must be expended at
See also:sea-level in the latitude of
See also:Greenwich in
See also:order to raise the temperature of one pound of water, weighed in vacuo, from 6o° to 61° F . Ultimately the discrepancy was traced to an error which, not by Joule's
See also:fault, vitiated the determination by the electrical method, for it was found that the standard
See also:ohm, as actually defined by the British Association committee and as used by him, was slightly smaller than was intended; when the necessary corrections were made the results of the two methods were almost precisely congruent, and thus the figure 772.55 was vindicated . In addition, numerous other researches stand to Joule's credit—the work done in compressing gases and the thermal changes they undergo when forced under pressure through small apertures (with
See also:Lord Kelvin), the
See also:change of
See also:volume on solution, the change of temperature produced by the
See also:longitudinal extension and compression of solids, &c . It was during the experiments involved by the first of these inquiries that Joule was incidentally led to appreciate the value of
See also:surface condensation in increasing the efficiency of the steam engine . A new
See also:form of
See also:condenser was tested on the small engine employed, and the results it yielded formed the starting-point of a series of investigations which were aided by a
See also:grant from the Royal Society, and were described in an elaborate memoir presented to it on the 13th of December 186o . His results, according to Kelvin, led directly and speedily to the
See also:practical method of surface-condensation, one of the most important improvements of the steam engine, especially for marine use, since the days of
See also:Watt . Joule died at Sale on the 11th of
See also:October 1889 . His scientific papers were collected and published by the
See also:Physical Society of
See also:London: the first volume, which appeared in 1884, contained the researches for which he was alone responsible, and the second, dated 1887, those which he carried out in association with other workers .
JOUGS, JUGGS, or JOGGS (O. Fr. joug, from Lat. jugu...
COUNT JEAN BAPTISTE JOURDAN (1762-1833)
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