own "New System of Chemical Philosophy." "Profound, patient, intuitive,"
his teaching must have had great influence on his pupils. We find Mr.
Joule early at work on the molecular constitution of gases, following in
the footsteps of his illustrious master, whose own investigations on the
constitution of mixed gases, and on the behavior of vapors and gases
under heat, were among the most important of his day, and whose
brilliant discovery of the atomic theory revolutionized the science of
chemistry and placed him at the head of the philosophical chemists of
Europe.

[Illustration: JAMES PRESCOTT JOULE.]

Under Dalton, Mr. Joule first became acquainted with physical apparatus;
and the interest excited in his mind very soon began to produce fruit.
Almost immediately he commenced experimenting on his own account.
Obtaining a room in his father's house for the purpose, he began by
constructing a cylinder electric machine in a very primitive way. A
glass tube served for the cylinder; a poker hung up by silk threads, as
in the very oldest forms of electric machine, was the prime conductor;
and for a Leyden jar he went back to the old historical jar of Cunaeus,
and used a bottle half filled with water, standing in an outer vessel,
which contained water also.

Enlarging his stock of apparatus, chiefly by the work of his own hands,
he soon entered the ranks as an investigator, and original papers
followed each other in quick succession. The Royal Society list now
contains, the titles of ninety-seven papers due to Joule, exclusive of
over twenty very important papers detailing researches undertaken by him
conjointly with Thomson, with Lyon Playfair, and with Scoresby.