and-sixtieth of the amount, and so on. Thus, when two stars are seen in
the field, one web is moved by the screw until the fixed line and the
movable one are parallel, each bisecting a star. By reading with the
microscope the number of degrees turned, the distance apart of the stars
becomes known; the distance being learned, position is then sought; the
observance of which led to one of the greatest discoveries ever made by
man. The permanent line of the micrometer is placed in the line joining
the north and south poles of the heavens, and brought across one of the
stars; the movable web is then rotated until it bisects the other, and
then the angle between the webs is recorded. Double stars are thus
measured, first in distance, and second, their position. After this, if
any movement of the stars takes place, the tell tale micrometer at once
detects it.

In 1780, Sir Wm. Herschel measured double stars and made catalogues with
distances and positions. Within twenty years, he startled intellectual
man with the statement that many of the fixed stars actually move--one
great sun revolving around another, and both rotating about their common
center of gravity. If we look at a double star with a small telescope,
it looks just like any other; using a little larger glass, it changes
appearance and looks elongated; with a still better telescope, they
become distinctly separated and appear as two beautiful stars whose
elements are measured and carefully recorded, in order to see if they
move. Herschel detected the motion of fifty of these systems, and
revolutionized modern astronomy. Astronomers soared away from the little
solar system, and began a minute search throughout the whole sidereal
heavens. Herschel's catalogue contained four hundred double suns, only
fifty of which were known to be in revolution. Since then, enormous
advance has been made. The micrometer has been improved into an
instrument of great delicacy, and the number of doubles has swelled to