370 PROPER MOTIONS OF THE STARS. SECT. XXXVII. 



there would be a regularity in these apparent motions 

 which would in time be detected ; but if the solar sys- 

 tem and the whole of the stars visible to us be carried 

 forward in space by a motion common to all, like ships 

 drifting in a current, it would be impossible for us, 

 moving with the rest, to ascertain its direction. There 

 can be no doubt of the progressive motion of the sun and 

 stars, but sidereal astronomy is not far enough advanced 

 to determine what relations these bear to one another ; 

 it will however be known in the course of time from the 

 orbits of the revolving stars of the binaiy systems. For 

 if the solar system be in motion, some of the stellar 

 orbits which, by the effects of perspective, appear to us 

 to be straight lines, will, after a time, open and become 

 elliptical by our change of place ; while others which 

 now appear to be open will close, or open wider ; stars 

 also which now occultate, or hide one another in certain 

 points of their orbits, will, in time, cease to do so. The 

 directions and magnitude of these changes will no doubt 

 show the motion of our system, to what point it is tend- 

 ing, and the velocity with which it moves. 



Among the multitudes of small stars, whether double 

 or insulated, a few are found near enough to exhibit 

 distinct parallactic motions, arising from the revolution 

 of the earth in its orbit. Of two stars apparently in 

 close approximation, one may be far behind the other in 

 space. These may seem near to one another when 

 viewed from the earth in one part of its orbit, but may 

 separate widely when seen from the earth in another 

 position, just as two terrestrial objects appear to be one 

 when viewed in the same straight line, but separate as 

 the observer changes his position. In this case the stars 

 would not have real, but only apparent motion. One of 

 them would seem to oscillate annually to and fro in a 

 straight line on each side of the other a motion which 

 could not be mistaken for that of a binary system, 

 where one star describes an ellipse about the other, or, 

 if the edge of the orbit be turned toward the earth, 

 where the oscillations require years for their accom- 

 plishment. 



This method of finding the distances of the fixed stars 

 was proposed by Galileo, and attempted by Dr. Long 



