372 THE STELLAE UNIVERSE. 



If phenomena like these were clearly ascertained among the stars, the mo- 

 tion of the solar system would be proved ; but on the other hand, such appear- 

 ances not being discovered, we must infer, not the quiescence of the system, 

 but the absence of any motion sufficiently rapid to produce an observable 

 effect on the apparent positions of bodies so distant as the fixed stars. In 

 a word, it must be concluded, that within the limited period of time over 

 which astronomical observation has extended, the space through which the 

 solar system has moved must bear an inappreciable ratio to the distances of 

 the stars. 



In the course of his various astronomical labors, the late Sir William Her- 

 schel imagined at one time that he had ascertained among the apparent changes 

 incidental to the firmament, indications of a movement of the solar system 

 toward a point of the universe occupied by some of the stars composing the 

 constellation of Hercules. This conjecture has not, however, been sustained 

 by subsequent surveys of the heavens ; and the opinion among astronomers 

 now is that no sufficient data have yet been attained to warrant any distinct 

 conclusion regarding the progressive motion common to the bodies of our 

 system. 



The late astronomer royal of England (Mr. Pond), suggested a mode of 

 investigating the motion of the solar system, marked by singular ingenuity 

 and refinement. It is known that the motion of light combined with that of 

 the earth in its annual orbit, produces an effect on the apparent places of all ob- 

 jects in the heavens, by which they are seen advanced beyond their true po- 

 sitions, always in the direction in which the earth is moving, and the extent 

 of this apparent displacement depends on the proportion which the earth's 

 orbitual velocity bears to the velocity of light. This effect is called the 

 aberration of light. Now if the sun, together with the planets, have any pro- 

 gressive motion through space, the velocity of such motion would probably be 

 much greater than the orbitual velocity of the earth. Such a motion would 

 then be attended with an aberration of the stars, greater in amount than that 

 which is due to the earth's motion. Such an aberration would cause all the 

 stars to be displaced to the same extent and in the same direction, and con- 

 sequently it would cause no change in their relative positions. We should 

 under such circumstances have no means of detecting it. But if, in the lapse 

 of ages, the velocity of the solar system were to undergo any change of suf- 

 ficient amount, or if the direction of its motion were to be changed (as would 

 certainly happen if our system were moving in an orbit round any other, owing 

 to any combination like those of the double stars), then the quantity or direc- 

 tion of the consequent aberration would be changed, the relative position of 

 the stars would be consequently disturbed, and the effects would become per- 

 ceptible. Such effects have not been yet observed, but this suggestion 

 may afford future astronomers the means of ascertaining the motion of our 

 system. 



But although no appearances have been discovered, such as a progressive 

 motion of our system would produce, yet other phenomena have been un- 

 folded which prove that the fixed stars are not absolutely stationary, and 

 which indicate physical powers in active operation in distant regions of 

 the universe, on a scale commensurate with the enormous distances and 

 magnitudes which telescopic research has unfolded. The stars, examined 

 individually with instruments of sufficient power and precision, have been 

 found to be subject to changes of position which, though small, are very 

 perceptible, and are certainly ascertained. These changes are called the 

 proper motions of the stars. 



These proper motions are not the same in all stars. In some no such motion 



