DELICATE SCIENTIFIC INSTRUMENTS. 745 
360° in a circle, 1-360th of a turn moves the web 1-36oth of the amount, and 
soon. 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 ifthey 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 400 double suns, only fifty of which were known to be in revolution. 
Since then, enormous advance has been made. The micrometer has been im- 
proved into an instrument of great delicacy, and the number of doubles has swelled 
to 10,000; 650 of them being known to be binary, or revolving on orbits—Prof, 
S.W. Burnham, the distinguished young astronomer of the Dearborn Observatory, 
Chicago, having discovered 800 within the last eight years. This discovery im- 
plies stupendous motion; every fixed star is a sun like our own, and we can 
imagine these wheeling orbs to be surrounded by cool planets, the abode of life, 
as well as ours. If the orbit of a binary system lies edgewise toward us, then one 
star will hide the other each revolution, moving across it and appearing on the 
other side. Several instances of this motion are known; the distant suns having 
made more than a complete circuit since discovery; the shortest periodic time 
known being twenty-five years. 
Wonderful as was this achievement of the micrometer, one not less surprising 
_awaited its delicate measurement. If one walks in a long street lighted with gas, 
the lights ahead will appear to separate, and those in the rear approach. The 
little spider lines have detected just such a movement in the heavens. The stars 
in Hercules are all the time growing wider apart, while those in Argus, in exactly 
the opposite part of the Universe, are steadily drawing. nearer together. This 
demonstrates that our sun with his stately retinue of planets, satellites, comets and 
