convenient."

The discovery by Faraday of the law of electro-chemical equivalents
had induced him to propose the voltameter as a measurer of electric
currents, but the system proposed had not been used in the researches
of any electrician, not excepting those of Faraday himself. Joule,
realizing for the first time the importance of having a system of
electric measurement which would make experimental results obtained
at different times and under various circumstances comparable among
themselves, and perceiving at the same time the advantages of a system
of electric measurement dependent on, or at any rate comparable with,
the chemical action producing the electric current, adopted as unit
quantity of electricity the quantity required to decompose nine grains
of water, 9 being the atomic weight of water, according to the chemical
nomenclature then in use.

He had already made and described very important improvements in the
construction of galvanometers, and he graduated his tangent galvanometer
to correspond with the system of electric measurement he had adopted.
The electric currents used in his experiments were thenceforth measured
on the new system; and the numbers given in Joule's papers from 1840
downward are easily reducible to the modern absolute system of electric
measurements, in the construction and general introduction of which
he himself took so prominent a part. It was in 1840, also, that after
experimenting on improvements in voltaic apparatus, he turned his
attention to "the heat evolved by metallic conductors of electricity and
in the cells of a battery during electrolysis." In this paper, and those
following it in 1841 and 1842, he laid the foundation of a new province
in physical science-electric and chemical thermodynamics-then totally
unknown, but now wonderfully familiar, even to the roughest common sense