Ampere
2 of the 6 encyclopedias on this shelf carry an entry for Ampere. Both are reproduced below, so you can see where they agree and where they differ.
Collier's New Encyclopedia (1921)
the practical unit of electric current strength. It is the measure of the current produced by an electro-motive force of one volt through a resistance of one ohm. In electric quantity it is the rate of one coulomb per second. AMPÈRE, ANDRÉ MARIE (äm-pār'), a French mathematician and physicist, was , after four years as a lecturer at Bourg born at Lyons in 1775. In 1805 and Lyons, he was called to Paris, where he distinguished himself as an able teacher in the Polytechnic School. In 1814 he became a member of the Academy of Sciences; in 1824 Professor of Experimental Physics in the Collégé de France. He died at Marseilles, June 10, 1836. Scientific progress is largely indebted to Ampère, especially for his electro-dynamic theory, and his original views of the identity of electricity and magnetism, as given in his "Collec- "Col tion of Electro-Dynamic Observations" (1822), and his "Theory of Electro- Dynamic Phenomena" (1830).
Aiton's Encyclopedia (1910)
am'par,Andre Marie (1775-1836), a French scientist. A native of Lyons. His father fell under the guillotine in 1793. Young Ampere was well educated and became a professor of physics in the University of Paris. A member of the French Institute, 1814. Several treatises by Ampere give him high place in the development of the science of electricity. His most renowned work is a Collection of Observations on Electro Dynamics, 1822. Ampere's discoveries in the field of science were remembered by giving his name to the unit of electrical current. An ampere is the current corresponding to an electromotive force of one volt moving through an ohm of resistance. It is about the current of a Daniell cell through thirty-nine feet of No. 24 copper wire.
What Has Changed in the Last Century
The biography holds up: Ampère was born at Lyons in 1775, died at Marseilles in 1836, and his 1820s electrodynamics remains foundational — Ampère's circuital law is one of the four Maxwell equations taught to every physics student. What has moved is the unit. Both accounts define the ampere the way Collier's did in 1921, as the current a volt drives through an ohm; in 1948 the international definition was changed to the force between two parallel current-carrying wires, and since 20 May 2019 the ampere has been fixed by the elementary charge, set exactly at 1.602176634 × 10⁻¹⁹ coulomb, so that one amp is a defined number of electrons per second. Aiton's homely gauge of 1910 — 'about the current of a Daniell cell through thirty-nine feet of No. 24 copper wire' — belongs to a vanished workshop world, while the amp itself is now stamped on every fuse and phone charger.
Written for this edition, 2026.