several ways. They have furnished inquirers with instruments of
precision; they have helped to develop accuracy of observation; best
of all, they have served ever to bring before the attention of men a
spectacle of the conditions in Nature which we term cause and effect.
The influence of these inventions on the development of learning has
been particularly great where the machines, such as our wind and water
mills, and our steam engine, make use of the forces of Nature,
subjugating them to the needs of man. Such instruments give an
unending illustration as to the presence in Nature of energy. They
have helped men to understand that the machinery of the universe is
propelled by the unending application of power. It was, in fact,
through such machines that men of science first came to understand
that energy, manifested in the natural forces, is something that
eternally endures; that we may change its form in our arts as its form
is changed in the operations of Nature, but the power endures forever.

It is interesting to note that the first observation which led to this
most important scientific conclusion that energy is indestructible
however much it may change its form, was made by an American, Benjamin
Thompson, who left this country at the time of the Revolution, and
after a curious life became the executive officer, and in effect king,
of Bavaria. While engaged in superintending the manufacture of cannon,
he observed that in boring out the barrel of the gun an amount of heat
was produced which evaporated a certain amount of water. He therefore
concluded that the energy required to do the boring of the metal
passed into the state of heat, and thus only changed its state, in no
wise disappearing from the earth. Other students pursuing the same
line of inquiry have clearly demonstrated what is called the law of
the conservation of energy, which more than anything has helped us to
understand the large operations of Nature. Through these studies we