542 BIBLIOGRAPHY OF HERSCHEL's WRITINGS. 



Herschel, W.: Sy^topsis op the Writings of— Continued. 



S. D. Yol. P. 



1787 77 229 In this latter case, though it maf be convenient to use expressions 

 which can only be justified by reasoning upon the facts themselves, 

 it will certainly be the safest way not to neglect a full description 

 of them, that it may appear to others how far we have been author- 

 ized to use the mental eye. 



1787 77 230 April 19, 1787, KS^ 36'° sidereal time, three volcanoes seen ; April 20, 



1787, lO"^ 2"" sidereal time, one of the three bums with greater vio- 

 lence than last night. The diameter of the volcano is twice that 

 of Jupiter's satellite III. 



231 The appearance of the actual fire exactly resembled a small piece of 



burning charcoal when it is covered with a very thin coat of white 

 ashes. All the adjacent parts of the volcanic mountain seemed to 

 be faintly illuminated by the eruption and were gradually more 

 obscure as they lay at a greater distance from the crater. This 

 eruption resembled much that which I saw on the 4th of May, 1783,* 

 an account of which I shall shortly lay before the society. 



William Herschel. 

 [Dated] Slough, near Windsor, April 21, 1787. 



232 Note on M. Mi<;CHAiN's comet. [1787,1.] 



1787 77 364 On the Georgian Planet and its satellites. By William Herschel, LL. D. 

 F. R. S. Read May 22, 1788. 

 In a former paper I gave the periodical times of two satellites revolv- 

 ing round the Georgian Planet in a general way. While it requires 

 a much longer series of observations than I have had an opportu- 

 nity of making to settle their mean motions with accuracy, I shall 

 communicate the result of my past observations, and believe that 

 the elements here delivered will be found to be full as accurate as 

 we can at this time expect. 

 365 Methods of measuring angles of position which were employed. 

 365 Synodical revolution of Satellite I = 8'i 17>i I'" 19.3". [Tjtania.] 



365 Synodical revolution of Satellite II = ISd ll'i S"" 1.5«. lOberon.'] 



366 Other elements. 



368 Mass of [ Uranus'] is 17.740612 times the earth's mass. 



369 Diameter of [ Uranus'] is assumed 4". 04625. 



370 Difficulties in making the measures of satellites stated. 



371 Measures of Satellite I and discussion of these. 



376 The light of these satellites is uncommonly faint. The second [ Ofteron] 



is the brighter of the two, but the diiference is not considerable. 



377 Elements of the orbits. W. Herschel. 



378 Plate V of diagrams. [Dated] Slough, March 1, 1788. 



1789 79 151 Observations on a Comet. In a letter from William Herschel, LL. D., 

 F. R. S., to Sir Joseph Banks, Bart., P. R. S. Read April 2, 1789. 

 Letter dated Slough, March 3, 1789. [This was comet 1788, II.] 

 151 The comet was discovered by Carolina Herschel, December 21, 



1788, and positions of it on December 22, 1788, are given. 



153 No solid nucleus, even so small as 1", could be seen, and the same fact 

 has been observed by me in three other comets. 

 1789 79 212 Catalogue of a second thousamd of New Nehulai and Clusters of Stars; 

 with a few introductory Bemarks on the Construction of the Heavent. 

 By William Herschel, LL. D., F. R. S. Read June 11, 1789. 

 213 A telescope has power to penetrate into space. Proof that every star 

 is a sun shining by its native brightness. 



•This observation is reported by Baron von TAcn in BoDli's Jahrbuch, 17S8, p. 144. 



