thoroughly practical was the scientific knowledge of the
universities and how much it led to important useful discoveries in
applied science and to anticipations of what is most novel even in our
present-day sciences. Some of these indeed are so startling, that only
that we know them not by tradition but from his works, where they may be
readily found without any doubt of their authenticity, we should be sure
to think that they must be the result of later commentators' ideas.
Bacon was very much interested in astronomy, and not only suggested the
correction of the calendar, but also a method by which it could be kept
from wandering away from the actual date thereafter. He discovered many
of the properties of lenses and is said to have invented spectacles and
announced very emphatically that light did not travel instantaneously
but moved with a definite velocity. He is sometimes said to have
invented gunpowder, but of course he did not, though he studied this
substance in various forms very carefully and drew a number of
conclusions in his observations. He was sure that some time or other man
would learn to control the energies exhibited by explosives and that
then he would be able to accomplish many things that seemed quite
impossible under present conditions.

He said, for instance:

Art can construct instruments of navigation, such that the
largest vessels governed by a single man will traverse rivers
and seas more rapidly than if they were filled with oarsmen.
One may also make carriages which without the aid of any
animal will run with remarkable swiftness.

In these days when the automobile is with us and when the principal
source of energy for motor purposes is derived from explosives of
various kinds, this expression of Roger Bacon represents a prophecy
marvellously surprising in its fulfilment. It is no wonder that the book
whence it comes bears the title "De Secretis Artis et Naturae." Roger
Bacon even went to the extent, however, of declaring that man would some
time be able to fly. He was even sure that with sufficient pains he
could himself construct a flying machine. He did not expect to use
explosives for his motor power, however, but thought that a windlass
properly arranged, worked by hand, might enable a man to make sufficient
movement to carry himself aloft or at least to support himself in the
air, if there were enough surface to enable him to use his lifting power
to adva