rents, the laws of which, had been established by Ampère for the permanent effects, and by Faraday for the transient effects produced by currents of induction. Weber found in them a new road and a personal glory. The series of memoirs in the Elektrodynamische Maasbestimmungen constitute an imperishable scientific monument, in which the extent of the descriptions may sometimes appear long to the reader eager to get on, but the attentive study of which is ever fruitful. It is impossible to give an adequate estimate of this work in a short analysis; we shall only point out a few of its salient traits. The invention of electrodynamometry, which depends on the reciprocal action of currents, permitted Weber to subject Ampère's law to a vigorous testing by a method that differed from that of Gauss only by the substitution 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 corresponding 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 expression Coulomb's laws of electrostatics. Ampère'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 establishing for the first time a close connection between phenomena that appear independent. Weber's labors are particularly distinguished 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 produced 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 weber 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-
