attributed the invention of
spectacles, the human race is his debtor. He described the true theory
of telescopes and microscopes, saying that lenses may be ground and
arranged in such a way as to render it possible to read the smallest
letters at incredible distances, and to count grains of sand and dust,
because of the magnitude of the angle under which we may perceive such
objects. He foresaw the greatest of all inventions in practical
astronomy--the application of optical means to instruments for the
measurement of angles. He proposed the propulsion of ships through the
water and of carriages upon roads by merely mechanical means. He
speculated upon the possibility of making a flying-machine. Admitting
the truth of alchemy, he advised the experimenter to find out the method
by which Nature makes metals and then to imitate it. He knew that there
are different kinds of air, and tells us that there is one which will
extinguish flame. These are very clear views for an age which mistook
the gases for leather-eared ghosts. He warned us to be cautious how we
conclude that we have accomplished the transmutation of metals, quaintly
observing that the distance between whitened copper and pure silver is
very great. He showed that air is necessary for the support of fire, and
was the author of the well-known experiment illustrating that fact by
putting a lighted lamp under a bell-jar and observing its extinction.

[Sidenote: Is persecuted and imprisoned.] There is no little
significance in the expression of Friar Bacon that the ignorant mind
cannot sustain the truth. He was accused of magical practices and of a
commerce with Satan, though, during the life of Clement IV., who was his
friend, he escaped without public penalties. This pope had written to
him a request that he would furnish him an account of his various
inventions. In compliance therewith, Bacon sent him the "Opus Majus" and
other works, together with several mathematical instruments which he had
made with his own hands. But, under the pontificate of Nicolas III., the
accusation of magic, astrology, and selling himself to the Devil was
again pressed, one point being that he had proposed to construct
astronomical tables for the purpose of predicting future events.
Apprehending the worst, he tried to defend himself by his work "De
Nullitate Magiae." "Because these things are beyond your comprehension,
you call them the works of the Devil; your theologians and canonist