472 THE POPULAR SCIENCE MONTHLY. 



of the sun, and the distance between them, from center to center, 

 is about eight million miles. 



The manner in which the spectroscope revealed the existence 

 of two stars in y8 Aurigse is a beautiful illustration of the unex- 

 pected and, so to speak, automatic application of an old principle 

 in the discovery of new facts not looked for. It was noticed at 

 the Harvard Observatory that the lines in the photographed spec- 

 trum of /? Auriga^ (and of a few other stars to be mentioned later) 

 appeared single in some of the photographs and double in others. 

 Investigation proved that the lines were doubled at regular inter- 

 vals of about two days, and that they appeared single in the in- 

 terim. The explanation was not far to seek. It is known that all 

 stars which are approaching us have their spectral lines shifted, 

 by virtue of their motion of approach, toward the violet end of 

 the spectrum, and that, for a similar reason, all stars which are 

 receding have their lines shifted toward the red end of the spec- 

 trum. Now, suppose two stars to be revolving around one another 

 in a plane horizontal, or nearly so, to the line of sight. When 

 they are at their greatest angular distance apart as seen from the 

 earth one of them will evidently be approaching at the same 

 moment that the other is receding. The spectral lines of the first 

 will therefore be shifted toward the violet, and those of the second 

 will be shifted toward the red. Then if the stars, when at their 

 greatest distance apart, are still so close that the telescope can not 

 separate them, their light will be combined in the spectrum ; but 

 the spectral lines, being simultaneously shifted in opposite direc- 

 tions, will necessarily appear to be doubled. As the revolution of 

 the stars continues, however, it is clear that their motion will 

 soon cease to be performed in the line of sight, and will become 

 more and more athwart that line, and as this occurs the spectral 

 lines will gradually assume their normal position and appear 

 single. This is the sequence of phenomena in ^ Aurigae. 



Such facts, like those connecting rows and groups of stars with 

 masses and spiral lines of nebula, present a terrible temptation to 

 speculation ; but who shall say that they do not also, like obscure 

 signlpoards, indicate the opening of a way which, starting in an 

 unexpected direction, nevertheless leads deep into the mysteries 

 of the universe ? 



Southward from fi we find the star 6, which is a beautiful quad- 

 ruple. We shall do best with our five-inch here, although in a 

 fine condition of the atmosphere the four-inch might suffice. The 

 primary is of the third magnitude ; the first companion is of mag- 

 nitude seven and a half, distance 2", p. 5 ; the second, of the tenth 

 magnitude, distance 45", p. 292 ; and the third, of the tenth mag- 

 nitude, distance 125", p. 350. 



We should look at the double 2 OKI with one of our larger 



