elusive source of this energy was muscular force, derived from compulsory human labor; and all the monuments and objects that have been left to us, as marks of ancient civilization, are the results of organized systems of slavery. The rock-sculptures of Elephanta, the Pyramids of Egypt, and the temples of Greece, were all the result of the labor of slaves, directed by the minds of freemen. It is said that a hundred thousand slaves were employed at one time in the construction of the Pyramids of Egypt; one hundred and twenty thousand were engaged in hewing the obelisks of Thebes, and an equal number in digging the ancient canal which joined the Nile and the Red Sea. These slaves were treated as beasts of burden, or as mere machines, of which Athens, in her palmy days, had four hundred thousand, with but twenty thousand freemen.
Now, we owe the abolition of this condition of humanity, in the higher civilized nations of the world at the present day, to the study of the laws of the operations of Nature. By a knowledge of these laws the energies of the elements of Nature are substituted for human labor, and by this substitution mankind is not only relieved from brute-labor, but also given control of energies which enable him to produce effects which could only result from the muscular power of beings of a superior order. It may be shown by a simple calculation that about fifteen tons of anthracite coal burned in the furnace of one of our best steam-engines exerts an energy equal to that of an able-bodied slave, working ten hours a day for thirty years of his active life. It is this substitution of the energies of Nature for the power of human muscle that, as we have said, has abolished slavery and elevated humanity to a higher plane than was ever dreamed of by the wisest sages of ancient times. To illustrate this, a few examples will suffice. As one of these, we may refer to the progress of the arts of locomotion, and the means which science has afforded for the instantaneous interchange of thought between men in the most distant parts of the earth; as another, to the production of clothing fabrics, in which a single individual, directing the energies of an engine of one-man power, is capable of doing three thousand times the work of an ordinary weaver. As a third example, we may point to the art of printing by means of the steam-press, in which a single man will make more copies in a given time of a composition, than a million of ancient transcribers could do. Science is every day creating new arts, and modifying and improving the processes of old ones. We are skeptical as regards the value of lost arts. It is true there are arts which have fallen into disuse, and others which depend upon the skill and patience of the individual, but none, which rests on any lost secret of Nature which science cannot restore.
The results we have mentioned are frequently attributed by superficial observation to immediate practical invention of persons having little or no knowledge of abstract science. But, in regard to this, it
