362 



SCIENCE. 



[N. S. Vol. XXII. No. 560. 



bility of air, that air thermometry became 

 adequately rigorous. On the theoretical 

 side Clapeyron (1834), Helmholtz (1847), 

 Joule (1848), had in various ways pro- 

 posed the use of the Carnot function (1894) 

 for temperature measurement, but the sub- 

 ject was finally disposed of by Kelvin 

 (1849, et seq.) in his series of papers on 

 temperature and temperature measure- 

 ment. 



Practical thermometry gained much from 

 the measurement of the expansion of mer- 

 cury by' Dulong and Petit (1818), re- 

 peated by Regnault. It also profited by 

 the determination of the viscous behavior 

 of glass, due to Pernet (1876) and others, 

 but more from the elimination of these 

 errors by the invention of the Jena glass. 

 It is 'significant to note that the broad 

 question of thermal expansion has yet no 

 adequate equation, though much has been 

 done experimentally for fluids by the mag- 

 nificent work of Amagat (1869, 1873, et 

 seq. ) . 



HEAT CONDUCTION. 



The subject of heat conduction from a 

 theoretical point of view was virtually 

 created by the great memoir of Fourier 

 (1822), which shed its first light here, but 

 subsequently illumined almost the whole of 

 physics. The treatment passed successive- 

 ly through the hands of many of the fore- 

 most thinkers, notably of Poisson (1835, 

 1837), Lame (1836, 1839, 1843), Kelvin 

 (1841-44) and others. With the latter 

 (1856) the ingenious method of sources 

 and sinks originated. The character of 

 the conduction is now well known for con- 

 tinuous media, isotropic or not, bounded by 

 the more simple geometrical forms, in par- 

 ticular for the sphere under all reasonable 

 initial and surface conditions. Much at- 

 tention has been given to the heat conduc- 

 tion of the earth, following Fourier, by 



Kelvin (1862, 1878), King (1893) and 

 others. 



Experimentally, Wiedemann and Franz 

 (1853) determined the relative heat con- 

 duction of metals and showed that for 

 simple bodies a parallel gradation exists 

 for the cases of heat and of electrical con- 

 ductivity. Noteworthy absolute methods 

 for measuring heat conduction were devised 

 in particular by Forbes (1842), F. Neu- 

 mann (1862), Angstrom (1861-64), and a 

 lamellar method applying to fluids by H. 

 F. Weber (1880). 



CALORIMETRY, 



Practical calorimetry was virtually com- 

 pleted by the researches of Black in 1763. 

 A rich harvest of experimental results, 

 therefore, has since accrued to the subjects 

 of specific, latent and chemical heats, due 

 in particularly important cases to ;the inde- 

 fatigable Eegnault (1840, 1845, et seq.). 

 Dulong and Petit (1819) discovered the 

 remarkable fact of the approximate con- 

 stancy of the atomic heats of the elements. 

 The apparently exceptional cases were in- 

 terpreted for carbon silicon and boron by 

 H. F. Weber (1875), and for sulphur by 

 Eegnault (1840). F. Neumann (1831) 

 extended the law to compound bodies and 

 Joule (1844) showed that in many cases 

 specific heat could be treated as additively 

 related to the component specific heats. 



Among recent apparatus the invention 

 of Bunsen's ice calorimeter (1870) de- 

 serves particular mention. 



THERMODYNAMICS. 



Thermodynamics, as has been stated, in 

 a singularly fruitful way interpreted and 

 broadened the old Leibnitzian principle of 

 vis viva of 1686. Beginning with the inci- 

 dental experiments of Rumford (1798) and 

 of Davy (1799) just antedating the cen- 

 tury, the new conception almost leaped 

 into being when J. R. Mayer (1842, 1845) 



