September 29, 1905. J 



SCIENCE. 



389 



replaced all others. Atmospheric elec- 

 tricity, after the memorable experiment of 

 Franklin (1751), made little progress until 

 Kelvin (1860) organized a systematic at- 

 tack. More recently a revival of interest 

 began with Exner (1886), but more par- 

 ticularly with Linss (1887), who insisted 

 on the fundamental importance of a de- 

 tailed knowledge of atmospheric conduc- 

 tion. It is in this direction that the recent 

 vigorous treatment of the atmosphere as 

 an ionized medium has progressed, owing 

 chiefly to the indefatigable devotion of 

 Elster and Geitel (1899, et seq.) and of 

 C. T. R. "Wilson (1897, et seq.). Quali- 

 tatively the main phenomena of atmos- 

 pheric electricity are now plausibly ac- 

 counted for; quantitatively there is as yet 

 very little specific information. 



VOLTA CONTACTS. 



Volta's epoch-making experiment of 1797 

 may well be added to the century which 

 made such prolific use of it; indeed, the 

 Voltaic pile (1800-02) and Volta's law of 

 series (1802) come just within it. Among 

 the innumerable relevant experiments Kel- 

 vin's dropping electrodes (1859) and his 

 funnel experiment (1867) are among the 

 more interesting, while the 'Spannungs- 

 reihe' of K Kohlrausch (1851, 1853) is the 

 first adequate investigation. Nevertheless, 

 the phenomenon has remained without a 

 universally acceptable explanation until 

 the present day, when it is reluctantly 

 yielding to electronic theory, although 

 ingenious suggestions like Helmholtz's 

 'Doppelschicht' (1879), the interpretations 

 of physical chemistry and the discovery 

 of the concentration cell (Helmholtz; 

 Nernst, 1888, 1889; Planck, 1890) have 

 thrown light upon it. 



Among the earliest theories of the gal- 

 vanic cell is Kelvin's (1851, 1860), which, 

 like Helmholtz's, is incomplete. The most 

 satisfactory theory is Nernst 's (1889). 



Gibbs (1878) and Helmholtz (1882) have 

 made searching critical contributions, 

 chiefly in relation to the thermal phe- 

 nomena. 



Volta's invention was made practically 

 efficient in certain famous galvanic cells, 

 among which Daniell's (1836), Grove's 

 (1839), Clarke's (1878), deserve mention, 

 and for the purposes of measurement 

 have been subserved by the potentiometers 

 of Poggendorff (1841), Bosscha (1855), 

 Clarke (1873). 



SEEBECK CONTACTS. 



Thermoelectricity, destined to advance 

 many departments of physics, was discov- 

 ered by Seebeck in 1821. The Peltier effect 

 followed in 1834, subsequently to be inter- 

 preted by Icilius (1853). A thermody- 

 namic theory of the phenomena came from 

 Clausius (1853) and with greater elabora- 

 tion, together with the discovery of the 

 Thomson effect, from Kelvin (1854, 1856), 

 to whom the thermoelectric diagram is due. 

 This was subsequently developed by Tait 

 (1872, et seq.) and his pupils. Avenarius 

 (1863), however, first observed the thermo- 

 electric parabola. 



The modern platinum-iridium or plati- 

 num-rhodium thermoelectric pyrometer 

 dates from about 1885 and has recently 

 been perfected at the Reichsanstalt. Mel- 

 loni (1835, et seq.) made the most efficient 

 use of the thermopyle in detecting minute 

 temperature differences. 



ELECTROLYSIS. 



Though recognized by Nichols and Car- 

 lisle (1800) early in the century, the laws 

 of electrolysis awaited the discovery of 

 Faraday (1834). Again, it was not till 

 1853 that further marked advances were 

 made by Hittorf 's (1853-59) strikingly 

 original researches on the velocities of the 

 ions. Later Clausius (1857) suggested an 

 adequate theory of electrolysis, which was 



