BIBLIOGRAPHY OF HEKSCHEL's WRITINGS. 527 



Herschel, W.: Synopsis of the WniTixcs of— Continued. 



A. D. Yol. P. 



all its planets and comets, may also have a motion toward some 

 particular point of the heavens. If this surmise should have any 

 foundation it will show itself in a series of some years in a kind 

 of systematical parallax or change due to the motion of the whole 

 solar system. 



1782 72 104 Theory of the annual parallax of double stars; General Postulata: 

 1. Let the stars be supposed, one with another, to be about the size 

 of the sun. 

 104 2. Let the difference of their apparent magnitudes be owing to their 

 different distances, so that a star of the 2d, 'M, 4th magnitude is 2, 

 3, 4 times as far off as one of the first. 



104 [Foot-note.] This is rather the order into which stars ought to be 



divided than that into which they are. And perhaps we ought to 

 make an allowance for some loss which may happen to the light of 

 very remote stars in its pass,age through immense tracts of space 

 most probably not quite destitute of some very subtle medium. 

 I have usually found very small telescopic stars to be red, or inchned 

 to red. 



105 Case of the parallax of stars in the ecliptic. 



106 The following general exi^ression for the parallax of two stars: 



Let P express the total iiarallax of a fixed star of the first magnitude ; 

 M the magnitude of the largest of the two stars; m the magnitude 

 of the smallest, and j; the iiartial parallax to be observed by the 



change in the distance of a double star : then will w = . P 



and p being found by observation will give us P = -^ , . 



107 Cases where the stars are not in the eclii^tic. 



1782 72 112 Cataloffuc of Donhle Stars. By Mr. Herschel, F. K. S., communicated 

 by Dr. Watsox, jun. Read January 10, 1782. 



112 Introductory remarks. The catalogue contains, I. The names of the 

 stars, etc. II. Their comparative size. HI. Their colors. IV. Thei j 

 distances, which are given several different ways. Those estimated 

 by the diameter can hardly be liable to an error of so much as 0".25. 

 Those measured by the micrometer may have errors from 1" to 2". 

 A new micrometer [Lamp-Micrometer, P. T., 1782, p. 163], made 

 within a few months, gives measures which can be relied on to 0".l 

 when a mean of three measures is taken. V. The angles of position ; 

 when measured they can be relied on to 2° or 3". VI. The dates of 

 discovery. 



115 Catalogue of Double Stars; First Class [24 stars]. 



120 h Draconis : " It is in vain to look for them if every circumstance is 

 not favorable. The observer as well as the instrument must have 

 been long enough out in the open air to acquire the same tempera- 

 ture. In very cold weather an hour at least will be required ; but 

 in a moderate temperature half an hour will be sutficient." 



122 Second Class of Double Stars [38 stars]. 



128 f Sagitice : the small star brighter with 460 than with 227 or 278. 



129 Third Class of Double Stars [46 stars]. 



131 7 DclpMni : " I suspect a motion in one of these stars. I thought it 

 best not to join other observations" to those of 1779. 

 ■ 136 Fourth Class of Double Stars [44 stars]. 

 142 Fifth Class of Double Stars [51 stars]. 



