PROGRESS IN NINETEENTH CENTURY 55 



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 Kelvin's dropping 

 electrodes (1859) and his funnel experiment (1867) are among 

 the more interesting, while the Spannungsreihe of R. Kohlrausch 

 (1851, 1853) is the first adequate investigation. Nevertheless, the 

 phenomenon has remained without a universally acceptable explana- 

 tion until the present day, when it is reluctantly yielding to electronic 

 theory, although ingenious suggestions like Helmholtz's Doppel- 

 schicht (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 galvanic 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 phenomena. 



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 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 discovered by Seebeck in 1821. The Peltier effect fol- 

 lowed in 1834, subsequently to be interpreted by Icilius (1853). A 

 thermodynamic theory of the phenomena came from Clausius (1853) 

 and with greater elaboration, together with the discovery of the 

 Thomson effect, from Kelvin (1854, 1856), to whom the thermo- 

 electric diagram is due. This was subsequently developed by Tait 

 (1872, et seq.) and his pupils. Avenarius (1863), however, first 

 observed the thermoelectric parabola. 



The modern platinum-iridium or platinum-rhodium thermo- 

 electric pyrometer dates from about 1885 and has recently been 

 perfected at the Reichsanstalt. Melloni (1835, et seq.) made the most 

 efficient use of the thermopyle in detecting minute temperature 

 differences. 



Electrolysis 



Though recognized by Nichols and Carlisle (1800) early in the 

 century, the laws of electrolysis awaited the discovery of Faraday 



