DELICATE SCIENTIFIC INSTRUMENTS. 747 
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 
¥%” to 8” annually. The Binary star, 61 Cygni, the nearest north of the equator 
moves 8” every year, a displacement equal in 360 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 never led 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 sun. 
light into seven colors and projects a band of light called a spectrum. This was. 
known for 300 years, and not much thought of it until Fraunhofer viewed it with 
a telescope, and was surprised to find it filled with hundreds of black lines in- 
visible to the unaided eye. Could it be possible that there are portions of the 
solar surface that fail to send out light? Such is the fact, and then begana 
twenty years search to learn the cause. The lines in the solar spectrum were 
unexplained until finally metals were vaporized in the intense heat of the elec- 
tric arc and the light passed through a spectroscope, when behold the spectra of 
metals were filled with bright lines in the same places as were the dark lines in 
the spectrum of the sun. Another step; if when metals are volatilized in the 
arc, rays of light from the sun are passed through the vapor and allowed to enter 
the spectroscope, a great change is wrought; a reversal takes place, and the 
original black bands reappear. A new law of nature was discovered, thus: 
“‘ Vapors of all elements absorb the same rays of light which they emit when 
incandescent.” Every element makes a different spectrum with lines in different 
places and of different widths. These have been memorized by chemists, so that 
when an expert having a spectroscope sees anything burn he can tell what it is 
as well as read a printed page. Men have learned the alphabet of the Universe, 
and can read, in all things radiating light, the constituent elements. The black 
lines in the solar spectrum are there because in the atmosphere of the sun exist 
vapors of metals, and the light from the liquid metals below is unable to pass 
through and reach the earth, being absorbed kind for kind. Gaseous iron sifts 
out all rays emitted from melted iron, and so do the vapors of all other ele- 
ments in the sun, radiating light in unison with their own. Sodium, iron, cal- 
cium, hydrogen, magnesium and many other substances are now known to be in- 
candescent in the sunand stars; andthe results of the developments of the spec- 
troscope may be summed up in the’ generalization that all bodies in the Universe 
are composed of the same substance the earth is. 
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