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THE SEVENTEENTH CENTURY. 351
are two distinct kinds of electricity one of which clings to
glass and the other to resin. Upon this followed improvements
of the apparatus for generating electricity brought
about by BOSE, J. H. WlNKLER and others and which led
to the construction of the electrical machine; the discovery
of the Leyden Jar made almost simultaneously
by. MUSSCHENBROEK at Leyden and Baron KLEIST in
Pomerania; the discovery of atmospheric electricity by LE
MONNIER; the invention of the lightning conductor by
BENJAMIN FRANKLIN; and the construction of the first
electrometer by JOHN CANTON.
Finally, certain other advances in physics must be mentioned
here, which belong to the same period. The thermometerwas
improved at the instigation of FERDINAND II. of the
Medici family. Already the differential thermometer was
invented. AMONTONS, who devised the hygroscope and
studied the influence of heat on the barometer, constructed
the first effective air-thermometer. By graduating and
adding a scale to the thermometer, for which FAHRENHEIT
of Danzig deserves special credit, its practical applicability
was largely extended. At Florence, the first observations
on specific heat were made ; it was called heat-capacity.
ALF. BORELLI threw more light upon the phenomena of
capillarity, a subject known to LEONARDO DA VlNCi.
But all these things yielded in importance to ISAAC
NEWTON'S discovery of general gravitation,* by which the
infinitely complicated movements of the heavenly bodies
were explained through the all-binding laws of mathematics
and physics and the proof was given that such laws hold
good for the entire universe. This conception exerted the
greatest influence in the emancipation of man's intellect
from the dominion of mystic transcendental powers, giving
it a grasp which seemed to reach beyond the boundaries of
this world. Even if NEWTON had rendered no other ser-
* W. WHEWELL ; History of the Inductive Sciences (Germ, trans.), Stuttgart
1840, ii, 158 el seq.