be exactly learned; but strange to say, photometers measure the quantity
of light that any bright body emits; hence the stars cannot have
specific gravity very far different from that of the sun, since they
send similar light, and in quantity obeying the law wherein light varies
inversely as the squares of distance. Therefore, knowing the weight and
having close approximation to density, the sizes of the stars are nearly
calculated. The conclusion is now made that all suns within the visible
universe are neither very many times larger nor smaller than our own.
(Newcomb and Holden's Astronomy, p. 454.)

Another result followed the use of the micrometer: the detection of the
proper motion of the stars. For several thousand years the stars have
been called "fixed," but the fine rulings of the filar micrometer tell a
different story. There are catalogues of several hundred moving stars,
whose motion is from one-half second to eight seconds annually. The
binary star, Sixty-one Cygni, the nearest north of the equator, moves
eight seconds every year, a displacement equal in three hundred and
sixty years to the apparent diameter of the moon. The fixed stars have
no general motion toward any point, but move in all directions.

Thus the micrometer revealed to man the magnitude and general structure,
together with the motions and revolutions of the sidereal heavens. Above
all, it demonstrated that gravity extends throughout the universe. Still
the longings of men were not appeased; they brought to view invisible
suns sunk in space, and told their weight, yet the thirst for knowledge
was not quenched. Men wished to know what all the suns are made of,
whether of substances like those composing the earth, or of kinds of
matter entirely different. Then was devised the spectroscope, and with
it men audaciously questioned nature in her most secluded recesses. The
basis of spectroscopy is the prism, which separates sunlight into seven