532 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschel, W.: Synopsis op the Writings of— Continued. 



A. D. Yol. p. 



1783 73 258 Here we ought to observe that it is not easy to prove a star to be 

 newly come. 

 259 "Does it not seem natural that these observations should cause a 

 strong suspicion that most probably every star in the heavens is 

 more or less in motion?" For though their proper motions could 

 not cause all these changes, yet we may well suppose that motion 

 is in some way concerned. 



259 A sjow motion, for instance, in an orbit round some opaque body 



might account for some of these changes, while others might be 

 owing to the periodical return of large spots, which become visi- 

 ble by a rotation. The idea also of a body flattened by a quick 

 rotation and having a motion whereby more of the luminous surface 

 would be exposed at one time than another tends to the same end. 



260 If the proper motion of the stars be admitted, who can deny that of 



our sun? Admitting this for granted, the greatest difficulty will 

 be to discern the proper motion of the sun between so many other 

 motions of the stars. This is an arduous task indeed, but we are 

 not to be discouraged in the attempt. Let us at all events en- 

 deavor to lay a good foundation for those who are to come after us. 

 I shall therefore now point out the method of detecting the direc- 

 tion and quantity of the supposed proper motion of the sun, and 

 show that we have already some reasons to guess which way the 

 solar system is probably tending its course. [See Figs. 1 and 2.] 



261 From the explanation of the figures it follows that — 



1. The greatest or total systematical parallax of the fixed stars will 

 fall upon those that are in the line DE at rectangles to the direc- 

 tion AB of the sun's motion. 



2. The partial systematical parallax of every other star [defined in 

 amount]. 



3. The parallax of stars at different distances will be inversely as 

 those distances. 



4. Every star at rest, to a system in motion, will appear to move in a 

 direction contrary to that in which the system is moviiig. 



Hence it follows that if the sun be carried toward any star in the 

 ecliptic, every star in [one half of the ecliptic] will decrease in 

 longitude, and every star in [the other half] will increase. 



262 No method is so proper for this purpose as to divide our observations 



into 3 zones, viz : the equator and the two colures, and double 

 stars are the most suitable for the purpose. Each of the 3 zones 

 [contains double stars, which are in the previous list]. 



263 The equatorial zone, 20° wide, contains 150 stars. [List of them 



given.] 



264 The zone of the equinoctial where 20° wide contains 70 double stars. 



[List given.] 



265 The zone of the solstitial where 20° wide contains 120 double stars. 



[List given.] 



266 A zone 20° wide of the ecliptic of 120 double stars may be added. 



[List given.] 



266 It remains now only for me to make an application of this theory to 



some of the facts we already know. 



267 And first let me observe that the rules of philosophizing direct us to 



refer all phenomena to as few and simple principles as are sufficient 

 to explain them. [An example given.] 



