SPECTRUM ANALYSIS. 



145 



been discovered by means of preparing charts of the lines of the terrestrial 

 elements, and comparing them with the lines of stella spectra. 



We have supposed the beam of light to enter through a slit in the 

 shutter, and fall upon a screen or sheet. The solar spectrum shown by the 

 passage of the beam through a prism is roughly as below 



170 



\ 'ello-M. Green. Bine, 



Fig. 151. Example of the Spectrum. 



Indigo. 



Violet. 



Fraunhofer substituted a telescope for the lens and the screen, and 

 called his instrument a SPECTROSCOPE. He then observed the lines, which 

 are always in the same position in the solar spectrum. The principal of 

 them he designated as A, B, C, D, E, F, G, H. The first three are in the red 

 part of the spectrum ; one in the yellow, then one in the green ; F comes 

 between green and blue, G in the indigo-blue, and H in the violet. But 

 these by no means exhaust the lines now visible. Year by year the study 

 of Spectrum Analysis has been perfected more and more, and now we are 

 aware of more than three thousand " lines " existing in the solar spectrum. 

 The spectra of the moon and planets contain similar dark lines as are seen 

 in the solar spectrum, but the fixed stars show different lines. By spectrum 

 analysis we know the various constituents of the sun's atmosphere, and we 

 can fix the result of our observations made by means of the Spectroscope 

 in the photographic camera. By the more recent discoveries great studies 

 have been made in " solar chemistry." 



What can we do with the Spectroscope, or rather, What can we not do ? 

 By Spectroscopy we can find out, and have already far advanced upon our 

 path of discovery, " the measure of the sun's rotation, the speed and direc- 

 tion of the fierce tornados which sweep over its surface, and give rise to the 

 * maelstroms ' we term ' sunspots,' and the mighty alps of glowing gas 

 that shoot far beyond the visible orb, ever changing their form and size ; 

 even the temperature and pressure of the several layers and their fluctuations 

 are in process of being defined and determined." This is what science is 

 doing for us, and when we have actually succeeded in ascertaining the 

 weather at various depths in the atmosphere of the sun, we shall be able to 

 predict our own, which depends so much upon the sun. Last year (1880) 

 Professor Adams, in his address to the British Association, showed that 

 magnetic disturbances, identical in kind, took place at places widely apart 

 simultaneously. He argues that the cause of these identical disturbances 

 must be far removed from the earth. 



" If," he says, " we imagine the masses of iron, nickel, and magnesium 

 in the sun to retain even in a slight degree their magnetic power in a 

 gaseous state, we have a sufficient cause for all our magnetic changes. We 



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