Photography of the Skies 



to bear images of Eros, impressed at intervals 

 for years before the discovery of the asteroid at 

 Berlin. These impressions indicate a considera- 

 able portion of the orbit of the object. Records 

 of equal value doubtless remain to be detected 

 in this remarkable portrait-gallery of the skies. 



In the moments which follow striking a match 

 in che dark, we see in succession the hues proper 

 to burning phosphorus, to sulphur, and to the 

 carbon of the match stick. In a display of fire- 

 works the combustibles are chosen for a display 

 of colour much more variegated and brilliant. 

 We recognize at once the yellow flame of sodium, 

 the crimson blaze of strontium, the purple glitter 

 of zinc aflame. These and all other elements 

 when they reach glowing heat give out light of 

 characteristic hues; to examine them minutely 

 a spectroscope is employed. In its essence this 

 instrument is a glass prism which sorts out with 

 consummate nicety the distinctions of colour and 

 line borne in the light of the sun, or a star, or a 

 meteor, or of the fuel ablaze in a laboratory 

 furnace Every ray as it passes through a prism 

 is deflected in a degree peculiar to its colour; 

 violet light, at one end of the rainbow scale, is 

 deflected most; red light, at the other end, is de- 

 flected least It is because solar and stellar 

 beams display the characteristic spectra of 

 sodium, iron, hydrogen, and many other terres- 

 trial elements, highly individualized as each of 

 them is, that we know that the sun and the stars 

 are built of much the same stuff as the earth. 

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