VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 325 



by its similar condition and situation, in the unbounded expanse of the starry 

 heavens, must often be the subject of the conversation, not only of astronomers, 

 but of every lover of science in general. This consideration then makes it 

 necessary to give it a name, by which it may be distinguished from the rest of 

 the planets and fixed stars. In the fabulous ages of ancient times the appellations 

 of Mercury, Venus, Mars, Jupiter, and Saturn, were given to the planets, as 

 being the names of their principal heroes and divinities. In the present more 

 philosophical sura, it would hardly be allowable to have recourse to the same 

 method, and call on Juno, Apollo, Pallas, or Minerva, for a name to our new 

 heavenly body. The first consideration in any particular event, or remarkable 

 incident, seems to be its chronology: if in any future age it should be asked, 

 when this last-found planet was discovered ? It would be a very satisfactory answer 

 to say, " In the reign of King George the Third." As a philosopher then, the 

 name of Georgium Sidus presents itself to me, as an appellation which will 

 conveniently convey the information of the time and country where and when it 

 was brought to view. 



11. On the Diameter and Magnitude of the Georgium Sidus; with a Description 

 of the Dark and Lucid Disc and Periphery Micrometers. By Wm. Herschel, 

 Esq., F.R.S. p. 4. 



In this paper Dr. H. describes several ingenious methods which he practised, 

 to obtain nearly the angle or apparent magnitude of his new planet. The mea- 

 sures of its diameter, which were delivered in his first paper, in 178], differ 

 considerably from each other. However, if we set aside the first 3, on a sup- 

 position that every minute object, which is much smaller than what we are 

 frequently used to see, will at first sight appear less than it really is; and take a 

 mean of the remaining observations, we shall have A" 36\'" for the diameter of 

 the planet. On comparing the measures then with this mean, we find but two 

 of them that differ somewhat more than half a second from it; the rest are 

 almost all within a quarter of a second of that measure. This agreement, in 

 the dimensions of any other planet, would appear very considerable; but not 

 being satisfied, when he thought it possible to obtain much more accurate mea- 



the diameter of this planet is about 35, 1 Of) miles, or 4-^ times that of the earth ; its distance from 

 the sun 1800 millions of miles, or above 1!) times the earth's distance ; and that the period of its 

 revolution in its orbit round the sun, is 83 years, 140 days, 17 hours. Dr. Herschel has 

 also discovered 6' satellites or moons belonging to this 

 planet, whose periodical revolutions are nearly as an- 

 nexed ; their orbits are nearly perpendicular to the 

 plane of the ecliptic ; and they all perform their re- 

 volutions in their oibits contrary to the order of the signs, 

 that is, their real motion is retrograde. 



