150 



SCIENTIFIC THOUGHT. 



there existed three different theories which aimed at 

 finding a general formula or law that should embrace 

 all known electro-dynamic phenomena. The two earlier 

 ones were propounded independently and about the same 



life. Du Bois-Reymond was a pupil 

 of Johannes Miiller. One of the 

 merits of Miiller's school was to 

 have made the discoveries of phy- 

 sics useful for physiology and medi- 

 cine as the school of Liebig made 

 those of chemistry. Helmholtz 

 was trained in the school of Muller, 

 but he also came largely under 

 the influence of Franz Neumann 

 of Konigsberg, the great teacher of 

 mathematical physics, and of Gauss 

 and Weber, the originators in Ger- 

 many of the system of absolute 

 measurements. It is known that 

 the interest in electrical phenomena 

 received a great impetus through 

 Galvani's and Volta's discoveries. 

 But as du Bois-Reymond (' Reden," 

 vol. ii. p. 389) tells us, the galvanic 

 pile constructed by Volta withdrew 

 attention from the phenomena of 

 animal electricity to the much 

 more powerful actions of artificial 

 arrangements of metals and solu- 

 tions. The study of animal electric- 

 ity was for a time continued only by 

 Italian professors, and beyond the 

 seas by Alexander von Humboldt 

 in his observations on the torpedo ; 

 and had to wait till the school 

 of Muller, and notably du Bois- 

 Reymond, approached the subject 

 methodically with the methods 

 and ideas of modern science. This 

 was in the fifth decade of the 

 century. Modern science in Ger- 

 many had, however, studied the 

 properties of the galvanic current 

 exhaustively only in linear (one 

 dimensional) and in closed circuits 

 or conductors. The phenomena of 

 nervous and muscular electric cur- 

 rents demanded the study of sud- 

 den and repeated electrical impulses, 

 and of the behaviour of currents 



in two and three dimensional con- 

 ductors, and in unclosed conductors 

 or circuits. Incited by du Bois- 

 Reymond, Helmholtz undertook to 

 deduce from the formulae of 

 Ampere, Neumann, and Weber the 

 action of electric currents in these 

 modified conditions. It was then 

 found that these formulae gave 

 indefinite results and required to 

 be modified or amplified. After 

 many years of thought and research 

 Helmholtz arrived at a generalisa- 

 tion which comprehended all the 

 different existing theories as special 

 cases. He then in addition to a 

 masterly mathematical discussion 

 betook himself to devise spe- 

 cial experiments to decide which 

 of the three possible expressions of 

 the general formula came nearest 

 the truth. A perusal of the me- 

 moirs contained in the first volume 

 of his ' Wissenschaftliche Abhand- 

 lungen ' (pp. 429-820) shows how 

 by gradual and strictly logical steps 

 he convinced himself of the in- 

 trinsic correctness of Faraday's con- 

 ception, which, in addition to the 

 phenomena in linear conductors or 

 wires, constantly took notice also of 

 those of the surrounding medium 

 or space i.e., of the electro- 

 magnetic field. Looking back from 

 our present position on the develop- 

 ment of the ideas concerning elec- 

 tricity in motion, we can say that 

 Continental thinkers tried to gain 

 a correcter and more complete un- 

 derstanding by a mathematical, 

 English science by a physical, ex- 

 tension of the then existing notions. 

 Helmholtz in his Faraday Lecture 

 (1881) showed how both courses, 

 consistently pursued, lead to the 

 same result. 



