And
this magnificent law, like that of the conservation of matter, is strong
evidence that there must have been a real Creation at some time in the
long ago, different not merely in degree but in kind from anything known
to modern science.
Joule worked out the mechanical equivalent of heat by means of his now
famous experiment of churning water. He reasoned that if the heat
produced by friction, etc., is really energy in another form, then the
same amount of heat must always be generated by the expenditure of a
given amount of motion or mechanical work. And this must be true, no
matter whether this work is expended in overcoming the friction between
wood on wood, iron on iron, or in any other conceivable way.
Accordingly, he devised an experiment in which paddle wheels were made
to rotate in a vessel of water by means of falling weights somewhat like
the weights of a clock. The amount of work represented by the falling of
the weights was easily calculated, and so was the amount of rise in
temperature of the water caused by the friction of the water with the
rotating paddle wheels. In various other ways he measured the amount of
heat generated by a measured amount of work; and as the result of all
his experiments (with very slight corrections made since by means of
more exact apparatus), we now know that 778 foot pounds of work produce
heat enough to raise one pound of water one degree Fahrenheit; or stated
in the metric system, 427 kilogram meters of work will produce a calorie
of heat.
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