260 Mr, herschel on the proper Motion 
alfo occafion motions of a different kind by a tranflation of tbe 
center Now, if the proper motion of the ftars in general 
be once admitted, who can refufe to allow that our fun, with 
all its planets and comets, that is, the folar fyftem, is no lefs 
liable to fuch a general agitation as we find to obtain among all 
the reft of the celeftial bodies +. 
Admitting this for granted, the greateft difficulty will be 
how to difeern the proper motion of the fun between fo many 
other (and varioufly compounded) motions of the ftars. Thid 
is an arduous talk indeed, which we muft not hope to fee ac- 
complifhed in a little time ; but we are not to be difcouraged 
from the attempt. Let us, at all events, endeavour to lay a 
good foundation for thofe who are to come after us. I fhall 
therefore now point out the method of detecting the direction 
and quantity of the fuppoled proper motion of the fun by a few 
geometrical deductions, and at the fame time ffiew by an appli- 
cation of them to fome known faCts, that we have already 
fome reafons to guefs which way the folar fyftem is probably 
tending its courfe. 
Suppofe the fun to be at S, fig. I. ; the fixed ftars to be dif- 
perfed in all poflible directions and diftarces around at s, s , s , s 9 
&c. Now, fetting alide the proper motion of the ftars, let us 
firft confider what will be the confequence of a proper motion 
in the fun ; and let it move in a direction from A towards B. 
* Relating to the motion of the fixed ftars, the Aftronomer Royal has an 
expreffion in the fecond page of the explanation and ufe of the tables publifhed in 
his Agronomical Obfcrvatlons, which feems to favour this idea, where he men- 
tions the “ peculiar but fmall motions, which many, if not all of them, 
“ have among thcmfelves, which have been called their proper motions, the caufes 
“ and laws of which are hid for the prefent in ahr.oft equal obfeurity.” 
See Mr. michell’s note, Phil. Tranf. vol. LVII. p. 252. 
4 
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