ted his experiments in their presence, but they set
aside the evidence of their senses and quoted Aristotle as much as
before. The enmity arising from these disputes rendered his situation so
unpleasant, that in 1592, at the invitation of the Venetian
commonwealth, he gladly accepted the professorship of mathematics at
Padua. The period of his appointment being only six years, he was
re-elected in 1598, and again in 1606, each time with an increase of
salary; a strong proof of the esteem in which he was held, even before
those astronomical discoveries which have immortalized his name. His
lectures at this period were so fully attended that he was sometimes
obliged to adjourn them to the open air. In 1609 he received an
invitation to return to his original situation at Pisa. This produced a
letter, still extant, from which we quote a catalogue of the
undertakings on which he was already employed. "The works which I have
to finish are principally two books on the 'System or Structure of the
Universe,' an immense work, full of philosophy, astronomy, and geometry;
three books on 'Local Motion,' a science entirely new, no one, either
ancient or modern, having discovered any of the very many admirable
accidents which I demonstrate in natural and violent motions, so that I
may, with very great reason, call it a new science, and invented by me
from its very first principles; three books of mechanics, two on the
demonstration of principles and one of problems; and although others
have treated this same matter, yet all that has been hitherto written,
neither in quantity nor otherwise, is the quarter of what I am writing
on it. I have also different treatises on natural subjects--on Sound and
Speech, on Light and Colors, on the Tides, on the Composition of
Continuous Quantity, on the Motions of Animals, and others besides. I
have also an idea of writing some books relating to the military art,
giving not only a model of a soldier, but teaching with very exact rules
everything which it is his duty to know, that depends upon mathematics,
as the knowledge of castrametation, drawing up of battalions,
fortification, assaults, planning, surveying, the knowledge of
artillery, the use of instruments, etc." Out of this comprehensive list,
the treatises on the universe, on motion and mechanics, on tides, on
fortification, or other works upon the same subjects, have been made
known to the world. Many, however, of Galileo's manuscripts, through