256 FRAGMENTS OF SCIENCE. 
might compare with those produced by our terrestrial 
metals, and prove either their identity or difference? No. 
The solar spectrum, when closely examined, gives us a 
multitude of fine dark lines instead of bright ones. They 
were first noticed by Dr. Wollaston, but were multiplied 
and investigated with profound skill by Fraunhofer, and 
named after him Fraunhofer's lines. They had been long 
a standing puzzle to philosophers. The bright lines 
yielded by metallic vapors had been also known to us for 
years; but the connection between both classes of phenom- 
ena was wholly unknown, until Kirchhoff, with admi- 
rable acuteness, revealed the secret, and placed it at the 
same time in our power to chemically analyze the sun. 
We have now some difficult work before us. Hitherto 
we have been delighted by objects which addressed them- 
selves as much to our sesthetic taste as to our scientific 
faculty; we have ridden pleasantly to the base of the final 
cone o"f Etna, and must now dismount and march through 
ashes and lava, if we would enjoy the prospect from the 
summit. Our problem is to connect the dark lines of 
Fraunhofer with the bright ones of the metals. The 
white beam of the lamp is refracted in passing through our 
two prisms, but its different components are refracted in 
different degrees, and thus its colors are drawn apart. 
Now the color depends solely upon the rate of oscillation 
of the atoms of the luminous body; red light being pro- 
duced by one rate, blue light by a much quicker rate, and 
the colors between red and blue by the intermediate rates. 
The solid incandescent coal-points give us a continuous 
spectrum; or in other words they emit rays of all possible 
periods between the two extremes of the spectrum. Color, 
as many of you know, is to light what pitch is to sound. 
When a violin-player presses his finger on a string he 
makes it shorter and tighter, and thus, causing it to vibrate 
more speedily, heightens the pitch. Imagine such a player 
to move his fingers slowly along the string, shortening it 
gradually as he draws his bow, the note would rise in pitch 
by a regular gradation; there would be no gap intervening 
between note and note. Here we have the analogue to 
the continuous spectrum, whose colors insensibly blend to- 
gether without gap or interruption, from the red of the 
lowest pitch to the violet of the highest. But suppose the 
player, instead of gradually shortening his string, to press 
