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Originally appearing in Volume V17, Page 934 of the 1911 Encyclopedia Britannica.
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JULIUS ROBERT MAYER (1814-1878), German physicist, was born at Heilbronn on the 25th of November 1814, studied medicine at Tubingen, Munich and Paris, and after a journey to Java in 1840 as surgeon of a Dutch vessel obtained a medical post in his native town. He claims recognition as an independent a priori propounder of the " First Law of Thermodynamics," but more especially as having early and ably applied that law to the explanation of many remarkable phenomena, both cosmical and terrestrial. His first little paper on the subject, " Bemerkungen giber die Krdfte der unbelebten Natur," appeared in 1842 in Liebig's Annalen, five years after the republication, in the same journal, of an extract from K. F. Mohr's paper on the nature of heat, and three years later he published Die organische Bewegung in ihren Zusammenhange mit dem Stoffwechsel. It has been repeatedly claimed for Mayer that he calculated the value of the dynamical equivalent of heat, indirectly, no doubt, but in a manner altogether free from error, and with a result according almost exactly with that obtained by J. P. Joule after years of patient labour in direct experimenting. This claim on Mayer's behalf was first shown to be baseless by W. Thomson (Lord Kelvin) and P. G. Tait in an article on " Energy," published in Good Words in 1862, which gave rise to a long but lively discussion. A calm and judicial annihilation of the claim is to be found in a brief article by Sir G. G. Stokes, Proc. Roy. Soc., 1871, p. 54. See also Maxwell's Theory of Heat, chap. xiii. Mayer entirely ignored the grand fundamental principle laid down by Sadi Carnot—that nothing can be concluded as to the relation between heat and work from an experiment in which the working substance is left at the end of an operation in a different physical state from that in which it was at the commencement. Mayer has also been styled the discoverer of the fact that heat consists in (the energy of) motion, a matter settled at the very end of the 18th century by Count Rumford and Sir H. Davy; but in the teeth of this statement we have Mayer's own words, " We might much rather assume the contrary—that in order to become heat motion must cease to be motion." 75", and consequently the longitude at sea to about half a degree. An improved set was afterwards published in London (1770), as also the theory (Theoria lunae juxta systema Newtonianum, 1767) upon which the tables are based. His widow, by whom they were sent to England, received in consideration from the British government a grant of £3000. Appended to the London edition of the solar and lunar tables are two short tracts—the one on determining longitude by lunar distances, together with a description of the repeating circle (invented by Mayer in 1V52), the other on a formula for atmospheric refraction, which applies a remarkably accurate correction for temperature. Mayer left behind him a considerable quantity of manuscript, part of which was collected by G. C. Lichtenberg and published in one volume (Opera inedita, Gottingen, 1775). It contains an easy and accurate method for calculating eclipses; an essay on colour, in which three primary colours are recognized; a catalogue of 998 zodiacal stars; and a memoir, the earliest of any real value, on the proper motion of eighty stars, originally communicated to the Gottingen Royal Society in 1760. The manuscript residue includes papers on atmospheric refraction (dated 1755), on the motion of Mars as affected by the perturbations of Jupiter and the Earth (1756), and on terrestrial magnet-ism (176o and 1762). In these last Mayer sought to explain the magnetic action of the earth by a modification of Euler's hypothesis, and made the first really definite attempt to establish a mathematical theory of magnetic action (C. Hansteen, Magnetismus der Erde, i. 283). E. Klinkerfuss published in 1881 photo-lithographic reproductions of Mayer's local charts and general map of the moon; and his star-catalogue was re-edited by F. Baily in 1830 (Memoirs Roy. Astr. Soc. iv. 391) and by G. F. J. A. Auvers in 1894. 934 Mayer's real merit consists in the fact that, having for himself made out, on inadequate and even questionable grounds, the conservation of energy, and having obtained (though by inaccurate reasoning) a numerical result correct so far as his data permitted, he applied the principle with great power and insight to the explanation of numerous physical phenomena. His papers, which were republished in a single volume with the title Die Mechanik der Warme (3rd ed., 1893), are of unequal merit. But some, especially those on Celestial Dynamics and Organic Motion, are admirable examples of what really valuable work may be effected by a man of high intellectual powers, in spite of imperfect information and defective logic. Different, and it would appear exaggerated, estimates of Mayer are given in John Tyndall's papers in the Phil. Mag., 1863–1864 (whose avowed object was " to raise a noble and a suffering man to the position which his labours entitled him to occupy "), and in E. Diihring's Robert Mayer, der Galilei des neunzehnten Jahrhunderts, Chemnitz, 1880. Some of the simpler facts of the case are summarized by Tait in the Phil. Mag., 1864, ii, 289.
End of Article: JULIUS ROBERT MAYER (1814-1878)

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