BIBLIOGRAPHY OF HERSCHEL'S WRITINGS. 541 



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



A.D. Tol. P. 



1787 77 125 An account of the discovery of tiro satellites revolving round the Georgian 

 Planet. By William Herschel, LL. D., F.R. S. Read Feb. 15, 1787. 



125 I had frequently directed large telescopes to this remote planet to see 



if it were attended by satellites, but failed for the want of sufficient 

 light in the instruments I used. 



126 In the beginning of [January, 1787] I found that my telescope used as 



a front view gave much more light. On the 11th of January I selected 

 a sweep which included the Georgian Planet, and noted down the 

 places of the small stars near it. The next day two of these were 

 missing. To satisfy myself I noted down all the small stars on the 

 14th, 17th, 18th, and 24th of January, and the 4th and 5th of Feb- 

 ruary, and though I had no longer any doubt of the existence of at 

 least one satellite, I thought it right to defer this communication 

 till I could see it actually in motion. Accordingly I began to pur- 

 sue this satellite on February the 7th, at about 6 o'clock in the eve- 

 ning, and kept it in view till three in the morning on Feb. the 8th, 

 and during those nine hours I saw this satellite faithfully attend its 

 primary planet and describe a considerable arc of its proper orbit. 



126 While I was attending to the motion of this satellite I did not forget 



to follow another small star which I was pretty well assured was 

 also a satellite. 



127 The first-discovered satellite [06ero«] is the farthest from the planet 



and I shall call it \he second satellite; the last-discovered [T/to/tm] I 

 shall call theirs* satellite. 



127 I made a sketch on paper to point out beforehand the situation of 



these satellites on Feb. 10, and [on that night] the heavens dis- 

 played the original of my drawing by shewing, in the situation I 

 had delineated them, the Georgian Planet attended by two satellites. 

 I confess that this scene appeared to me with additional beauty as 

 the little secondary planets seemed to give a dignity to the primary 

 one which raises it into a more conspicuous situation among the 

 great bodies of our solar system. 



128 I suppose the first performs a synodical revolution in about 8f days, 



the second in nearly 134- days. Their orbits make a considerable 

 angle with the ecliptic. 



129 Attempts to measure them with my micrometers have so far failed. 



I have nevertheless several resources in view and do not despair of 

 succeeding pretty well in the end. ^^^ Herschel. 



[Dated] Slough, near Windsor, February 11, 1787. 



1787 77 229 An account of Three Volcanoes in the Moon. By W^illiam Herschel, 

 LL. D., F. R. S.; communicated by Sir Joseph Banks, Bart., P. R. 

 S. Read April 26, 1787. 

 229 The phenomena of nature are to be viewed not only with the usual 

 attention to facts as they occur, but with the eye of reason and ex- 

 perience. In this we are not allowed to depart from plain appear- 

 ances. Thus when we see on the surface of the moon a great num- 

 ber of elevations from half a mile to a mile and a half in height we 

 are strictly entitled to call them mountains ; but when we attend 

 to ^heir particular shape, in which many of them resemble the 

 craters of our volcanoes, and thence argue that they owe their 

 origin to the same cause which has modeled many of these, we may 

 be said to see by analogy, or with the eye of reason. 



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