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SCIENCE. 



[N. S. Vol. XXII. No. 561. 



subsequently to be specialized in the disso- 

 ciation hypothesis of Arrhenius (1881, 

 1884). To the elaborate investigations of 

 F. Kohlrausch (1879, et seq.), however, 

 science owes the fundamental law of the 

 independent velocities of migration of the 

 ions. 



Polarization discovered by Ritter in 1803 

 became in the hands of Plante (1859-1879) 

 an invaluable means for the storage of 

 energy, an application which was further 

 improved by Faure (1880). 



STEADY FLOW. 



The fundamental law of the steady flow 

 of electricity, in spite of its simplicity, 

 proved to be peculiarly elusive. True, 

 Cavendish (1771-81) had definite notions 

 of electrostatic resistance as dependent on 

 length section and potential, but his intui- 

 tions were lost to the world. Davy (1820), 

 from his experiments on the resistances of 

 conductors, seems to have arrived at the 

 law of sections, though he obscured it in a 

 misleading statement. Barlow (1825) and 

 Becquerfil (1825-26), the latter operating 

 with the ingenious differential galvanom- 

 eter of his own invention, were not more 

 definite. Surface effects were frequently 

 suspected. Ohm himself, in his first paper 

 (1825), confused resistance with the polar- 

 ization of his battery, and it was not till 

 the next year (1826) that he discovered 

 the true law, eventually promulgated in 

 his epoch-making 'Die galvanische Kette' 

 (1827). 



It is well known that Ohm's mathemat- 

 ical deductions were unfortunate, and 

 would have left a gap between electro- 

 statics and voltaic electricity. But after 

 Ohm's law had been further experiment- 

 ally established by Fechner (1830), the 

 correct theory was given by Kirchhoff 

 (1849) in a way to bridge over the gap 

 specified. Kirchhoff approached the ques- 

 tion gradually, considering first the distri- 



bution of current in a plane conductor 

 (1845-1846), from which he passed to the 

 laws of distribution in branched conductors 

 (1847-48) — laws which now find such uni- 

 versal application. In his great paper, 

 moreover, Kirchhoff gives the general equa- 

 tion for the activity of the circuit and from 

 this Clausius (1852) soon after deduced 

 the Joule effect theoretically. The law, 

 though virtually implied in Riess's results 

 (1837), was experimentally discovered by 

 Joule (1841). 



As bearing critically or otherwise on 

 Ohm's law we may mention the researches 

 of Helmholtz (1852), of Maxwell (1876), 

 the solution of difficult problems in regard 

 to terminals or of the resistance of special 

 forms of conductors, by Rayleigh (1871, 

 1879), Hicks (1883) and others, the discus- 

 sion of the refraction of lines of flow by 

 Kirchhoff (1845), and many researches on 

 the limits of accuracy of the law. 



Finally, in regard to . the evolution of 

 the modern galvanometer from its inven- 

 tion by Schweigger (1820), we may enu- 

 merate in succession Nobili's astatic sys- 

 tem (1834), Poggendorff's (1826) and 

 Gauss's (1833) mirror device, the aperiodic 

 systems, Weber's (1862) and Kelvin's 

 critical study of the best condition for 

 galvanometry, so cleverly applied in the 

 instruments of the latter. Kelvin 's siphon 

 recorder ( 1867 ) , reproduced in the Depretz- 

 D 'Arsonval system ( 1882 ) , has adapted the 

 galvanometer to modern conditions in cities. 

 For absolute measurement Pouillet's tan- 

 gent galvanometer (1837), treated for abso- 

 lute measurement by Weber (1840), and 

 Weber's dynamometer (1846) have lost 

 little of their original importance. 



MAGNETISM. 



Magnetism, definitely founded by Gilbert 

 (1600) and put on a quantitative basis by 

 Coulomb (1785), was first made the sub- 

 ject of recondite theoretical treatment by 



