552 THE POPULAR SCIENCE MONTHLY. 



rents, tlie laws of which, had been established by Ampere for the 

 permanent effects, and by Faraday for the transient effects pro- 

 duced by currents of induction. Weber found in them a new 

 road and a personal glory. The series of memoirs in the Elehtro- 

 dynamische Maashestimmungen constitute an imperishable scien- 

 tific monument, in which the extent of the descriptions may some- 

 times appear long to the reader eager to get on, but the attentive 

 study of which is ever fruitful. It is impossible to give an ade- 

 quate estimate of this work in a short analysis ; we shall only 

 point out a few of its salient traits. The invention of electro- 

 dynamometry, which depends on the reciprocal action of currents, 

 permitted Weber to subject Ampere's law to a vigorous testing 

 by a method that differed from that of Gauss only by the substi- 

 tution of coils for magnets. The close study of the deviations 

 produced in galvanometric apparatus by permanent or temporary 

 currents furnished him with a means of devising precise methods 

 of observation, of measuring quantities of electricity correspond- 

 ing to the discharge by the impulse impressed by them on the 

 magnetic needle, and of estimating the approximate duration of 

 the discharges by a combination of the galvanometer and the 

 electrodynamometer. 



In the course of his experimental researches, Weber made 

 known an important formula which includes in a single expres- 

 sion Coulomb's laws of electrostatics. Ampere's laws on the 

 reciprocal action of currents, and the phenomena of induction 

 described by Faraday. Gauss seems not to have been a stranger 

 to the selection of this formula, and the theoretical conceptions 

 which are its basis may give occasion to discussion ; but Weber 

 has the merit of having shown all its consequences by establish- 

 ing for the first time a close connection between phenomena that 

 appear independent. Weber's labors are particularly distin- 

 guished by the introduction of the absolute measures which have 

 contributed for several years to the rapid progress of electricity 

 as a subject of pure science and in its industrial applications. To 

 him, in fact, we owe the suppression of a vague terminology in 

 which currents were estimated by the kind of piles and number 

 of couples, the length and size of circuits, or the deviation pro- 

 duced in a dynamometer of which only the number of turns of wire 

 was indicated. The inestimable services that have been derived 

 from the employment of absolute measures justify the attribution 

 of the name of weher to the unity of the current as defined by its 

 electromagnetic action, for which the mechanical unities of Gauss 

 — the millimetre, the milligramme, and the second of mean time 

 — are adopted. 



Weber's biographer in Nature gives Sir William Thomson the 

 credit of having been one of the first men of science to recog- 



