being rubbed affected the needle. In this way he discovered that
light substances were attracted by alum, mica, arsenic,
sealing-wax, lac sulphur, slags, beryl, amethyst, rock-crystal,
sapphire, jet, carbuncle, diamond, opal, Bristol stone, glass,
glass of antimony, gum-mastic, hard resin, rock-salt, and, of
course, amber. He discovered also that atmospheric conditions
affected the production of electricity, dryness being unfavorable
and moisture favorable.

Galileo's estimate of this first electrician is the verdict of
succeeding generations. "I extremely admire and envy this
author," he said. "I think him worthy of the greatest praise for
the many new and true observations which he has made, to the
disgrace of so many vain and fabling authors."


STUDIES OF LIGHT, HEAT, AND ATMOSPHERIC PRESSURE

We have seen that Gilbert was by no means lacking in versatility,
yet the investigations upon which his fame is founded were all
pursued along one line, so that the father of magnetism may be
considered one of the earliest of specialists in physical
science. Most workers of the time, on the other band, extended
their investigations in many directions. The sum total of
scientific knowledge of that day had not bulked so large as to
exclude the possibility that one man might master it all. So we
find a Galileo, for example, making revolutionary discoveries in
astronomy, and performing fundamental experiments in various
fields of physics. Galileo's great contemporary, Kepler, was
almost equally versatile, though his astronomical studies were of