408 Dynamic Theory. 



the F line toward the red end in one case and the violet end in the other. 

 The velocity of these storms is sometimes 100 miles per second. The 

 hydrogen lines chiefly are affected by these storms, but the sodium, iron 

 and magnesium lines are sometimes similarly affected. Many of the 

 "fixed" stars examined by the spectroscope are in the same way found 

 to be loose. In order to ascertain whether a line, the F line for example, 

 of the spectrum of a star is out of place, it is necessary to introduce 

 into the same spectroscope the spectrum of hydrogen, so as to have the 

 two spectra side by side for comparison. This is done by an ingenious 

 arrangement, and by these comparisons a great many stars have been 

 found to be in motion either toward or away from our sun. In most 

 cases the comparison was made with hydrogen, in one with sodium, and 

 in several cases with magnesium. 



The following are moving away from the sun : Sirius at the rate of 

 20 miles per second ; Betelgeux, 22 miles per second; Rigel, 15; Cas- 

 tor, 25; Regulus, 15 ; five stars in the constellation of the Great Bear, 

 19 ; nine other stars, including Aldebaran, at various rates. The fol- 

 lowing are approaching the sun : Arcturus, 55 miles per second ; Vega, 

 50 ; Alpha C} T gni, 39 ; Pollux, 49 ; Alpha, in the constellation of the 

 Great Bear, 53 ; and six others at rates not given. ( Lockyer. ) 



There are some gases, some liquids and some solid bodies through 

 which, at their ordinary temperature, it is possible to send a beam of 

 light. If such beam, after passing through the body, is passed through 

 a prism and made to form a spectrum, there will be the peculiar dark 

 lines across the spectrum, due to the absorption of certain ra3*s by the 

 body. This fact is of great use to the chemist, who can, by that means, 

 detect the presence of a substance in a compound or a solution, which 

 it would be difficult to find in any other way. The air, with its con- 

 tained gases, moisture, &c. , has its peculiar lines of absorption which 

 the astronomer is obliged to take account of. Thus we see there is no 

 body of matter, big or little, that is exempt from the impact of the en- 

 ergy of ether in undulation, and there is none, big or little, that fails to 

 deflect or re-direct, or to modify or re-form the energy and give it a dif- 

 ferent appearance. It is scarcely possible to conceive of a particle of 

 matter so small as to be unable to make its mark across the spectrum. 

 Nor can any imagination realize the distance across space, which is 

 traversed by a ray that is shot from the sodium vapor of a fixed star to 

 mark the " D line " in the little spectroscope of a mundane astronomer. 

 Such ray may have received its send-off years before it reached the spec- 

 troscope. And of the myriads of other rays that started with it, a 

 great number have fallen upon the earth and been degraded to heat, 

 while the great majority have missed the earth and will travel on till 

 intercepted by some other world. 



