icipated Harvey's discovery of the
circulation of the blood. Unfortunately, as the matter is of interest,
Servetus's treatment of the subject, found in his work on _The
Trinity_, is too long to quote, but it is plain that, along with
various fallacious ideas, he had really discovered the truth that the
blood all passes through heart and lungs whence it is returned to the
other organs.

[Sidenote: Physics]

While hardly anything was done in chemistry, a large number of
phenomena in the field of physics were observed now for the first time.
Leonardo da Vinci measured the rapidity of falling bodies, by dropping
them from towers and having the time of their passage at various stages
noted. He thus found, correctly, that their velocity increased. It is
also said that he observed that bodies always fell a little to the
eastward of the plumb line, and thence concluded that the earth
revolved on its axis. He made careful experiments with billiard balls,
discovering that the {614} momentum of the impact always was preserved
entire in the motion of the balls struck. He measured forces by the
weight and speed of the bodies and arrived at an approximation of the
ideas of mechanical "work" and energy of position. He thought of
energy as a spiritual force transferred from one body to another by
touch. This remarkable man further invented a hygrometer, explained
sound as a wave-motion in the air, and said that the appearance known
to us as "the old moon in the new moon's lap" was due to the reflection
of earth-light.

Nicholas Tartaglia first showed that the course of a projectile was a
parabola, and that the maximum range of a gun would be at an angle of
45 degrees.

Some good work was done in optics. John Baptist della Porta described,
though he did not invent, the camera obscura. Burning glasses were
explained. Leonard Digges even anticipated the telescope by the use of
double lenses.

Further progress in mechanics was made by Cardan who explained the
lever and pulley, and by Simon Stevin who first demonstrated the
resolution of forces. He also noticed the difference between stable
and unstable equilibrium, and showed that the downward pressure of a
liquid is independent of the shape of the vessel it is in and is
dependent only on the height. He and other scholars asserted the
causation of the tides by the moon.

[Sidenote: Magnetism]

Magnetism was much studied. When compasses were first invented it was
tho