TRANSLATORY MOTION. 14T 



the concatenation of causes if there were not one primordiai 

 immovable motor."* 



The manifold translatory changes of the stars, not those 

 produced by the parallaxes at which they are seen from the 

 changing position of the spectator, but the true changes con- 

 stantly going on in the regions of space, afford us incontro- 

 vertible evidence of the dominion of the laws of attraction in 

 the remotest regions of space, beyond the limits of our solar 

 system. The existence of these laws is revealed to us by 

 many phenomena, as, for instance, by the motion of double 

 stars, and by the amount of retarded or accelerated motion in 

 different parts of their elliptic orbits. Human inquiry need 

 no longer pursue this subject in the domain of vague conjec- 

 ture, or amid the undefined analogies of the ideal world ; for 

 even here the progress made in the method of astronomical 

 observations and calculations has enabled astronomy to take 

 up its position on a firm basis. It is not only the discovery 

 of the astounding numbers of double and multiple stars re- 

 volving round a center of gravity lying ivitliout their system 

 (2800 such systems having been discovered up to 1837), but 

 rather the extension of our knowledge regarding the funda- 

 mental forces of the whole material world, and the proofs we 

 have obtained of the universal empire of the laws of attrac- 

 tion, that must be ranked among the most brilliant discoveries 

 of the age. The periods of revolution of colored stars present 

 the greatest differences ; thus, in some instances, the period 

 extends to 43 years, as in 7\ of Corona, and in others to sev- 

 eral thousands, as in 66 of Cetus, 38 of Gemini, and 100 of 

 Pisces. Since Herschel's measurements in 1782, the satellite 

 of the nearest star in the triple system of ^ of Cancer has com- 

 pleted more than one entire revolution. By a skillful com- 

 bination of the altered distances and angles of position,! the 

 elements of these orbits may be found, conclusions drawn re- 

 garding the absolute distance of the double stars from the 

 Earth, and comparisons made between their mass and that 

 of the Sun, Whether, however, here and in our solar sys- 

 tem, quantity of matter is the only standard of the amount 

 of attractive force, or whether specific forces of attraction pro- 

 portionate to the mass may not at the same time come into 

 operation, as Bessel was the first to conjecture, are questions 



* Aristot., de Caelo, iii., 2, p. 301, Bekker ; Phys., viii., 5, p. 256. 



t Savary, in the Connaissance des Terns, 1830, p. 56 and 163. Encke, 

 Berl. Jahrb.. 1832, s. 253, &c. Arago, in the Annuaire, 1834, p. 260 

 295. John Herschel, in the Memoirs of the Astronom. Soc, vol. v., p. 17 1 



