When Sir Humphry Davy was studying medicine at Penzance, one of his
constant associates was Mr. Tom Harvey, a druggist in the above town.
They constantly experimented together; and one severe winter’s day,
after a discussion on the nature of heat, the young philosophers were
induced to go to Larigan river, where Davy succeeded in developing heat
by _rubbing two pieces of ice together_ so as to melt each other;[44]
an experiment which he repeated with much _éclat_ many years after,
in the zenith of his celebrity, at the Royal Institution. The pieces
of ice for this experiment are fastened to the ends of two sticks,
and rubbed together in air below the temperature of 32°: this Davy
readily accomplished on the day of severe cold at the Larigan river;
but when the experiment was repeated at the Royal Institution, it was
in the vacuum of an air-pump, when the temperature of the apparatus and
of the surrounding air was below 32°. It was remarked, that when the
surface of the rubbing pieces was rough, only half as much heat was
evolved as when it was smooth. When the pressure of the rubbing piece
was increased four times, the proportion of heat evolved was increased
sevenfold.