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who were powerful agents in bringing it about, were all born during the
fifteenth century, four of them at least, at so nearly the same time as
to be contemporaries.

Leonardo da Vinci, whose artistic genius has charmed succeeding
generations, was also the first practical engineer of his time, and the
first man after Archimedes to make a substantial advance in developing
the laws of motion. That the world was not prepared to make use of his
scientific discoveries does not detract from the significance which
must attach to the period of his birth.

Shortly after him was born the great navigator whose bold spirit was to
make known a new world, thus giving to commercial enterprise that
impetus which was so powerful an agent in bringing about a revolution
in the thoughts of men.

The birth of Columbus was soon followed by that of Copernicus, the
first after Aristarchus to demonstrate the true system of the world. In
him more than in any of his contemporaries do we see the struggle
between the old forms of thought and the new. It seems almost pathetic
and is certainly most suggestive of the general view of knowledge taken
at that time that, instead of claiming credit for bringing to light
great truths before unknown, he made a labored attempt to show that,
after all, there was nothing really new in his system, which he claimed
to date from Pythagoras and Philolaus. In this connection it is curious
that he makes no mention of Aristarchus, who I think will be regarded
by conservative historians as his only demonstrated predecessor. To the
hold of the older ideas upon his mind we must attribute the fact that
in constructing his system he took great pains to make as little change
as possible in ancient conceptions.

Luther, the greatest thought-stirrer of them all, practically of the
same generation with Copernicus, Leonardo and Columbus, does not come
in as a scientific investigator, but as the great loosener of chains
which had so fettered the intellect of men that they dared not think
otherwise than as the authorities thought.

Almost coeval with the advent of these intellects was the invention of
printing with movable type. Gutenberg was born during the first decade
of the century, and his associates and others credited with the
invention not many years afterwards. If we accept the principle on
which I am basing my argument, that in bringing out the springs of our
progress we should assign the first place to the birt