522 JRoml Astronomical Society. 



was much astonished to find its magnitude superior, not only to that 

 of Fomalhaut and a Crucis (with which stars it no longer admits of 

 a moment's comparison), but even to that of Aldebaran, Procyon, a 

 Eridani, a Ononis, and little if at all inferior to that of Rigel. 



*' This was my own judgement, and that of several persons whom 

 I called to my assistance, in the early part of the night, when rj 

 was low and Rigel high in the heavens. At the time I write, they 

 have about equal altitudes, and the comparison is decidedly in 

 favour of rj, which is, in fact (Sirius and Canopus excepted), the 

 most brilliant star now visible ; a Centauri being too low for fair 

 comparison, and veiled with some degree of haze. 



" This remarkable increase of magnitude has come on very sud- 

 denly, as my attention has frequently of late been drawn to this star 

 in the lower part of its diurnal circle, while watching with some 

 impatience its progress towards the meridian, at a reasonable hour 

 of the night, that I might resume and complete, before my depart- 

 ure hence, a very elaborate monograph of the wonderful nebula 

 which surrounds it. A few evenings before the full moon just passed, 

 in particular, I remember to have noticed it with this view ; and had 

 it then been what it now is, a star of the first class, it could not have 

 passed unremarked. 



" Whether it be now at its maximum, and about to decrease by 

 insensible degrees ; whether, like Algol, but in a much longer time, 

 it remains as it were dormant through the greater part of its period, 

 and runs through its phases of increase and decrease in a small 

 aliquot portion of the whole ; or whether, lastly, it be on the point 

 of blazing forth with extraordinary splendour, so as possibly to out- 

 shine its brilliant neighbours, a Centauri and Canopus, it is useless 

 to conjecture, and observation will soon determine." 



III. Value of the Mass of Uranus, deduced from Observations of 

 its Satellites, made at the Royal Observatory of Munich during the 

 year 1837. By Dr. F. Lamont, Director of the Royal Observatory. 



In the course of the year 1837, a few favourable nights were em- 

 ployed in taldng observations of the satellites of Uranus, with a view 

 of calculating the value of the planet's mass ; and, though the ob- 

 ject has not been satisfactorily attained, owing to the difiiculty of 

 the observations, and the present unfavourable position of the orbits 

 of the satellites, the result is not without interest, as it leads to the 

 conclusion that the true value of the mass of Uranus is considerably 

 smaller than that which is generally adopted. 



The instrument used in the observations was a refractor con- 

 structed at Munich, having a focal length of 15 feet, and an aper- 

 ture of IQi inches, Paris measure. The fact of its having served 

 to measure the distances of the satellites of Uranus is sufficient evi- 

 dence of its superior power. Dr. Lamont acknowledges, however, 

 that, notwithstanding the great optical power of the telescope, he 

 has not, as yet, been able to discover more than three of the satel- 

 lites, namely, the second, the fourth, and the sixth*. The sixth 



* The satellites are named in the order of their distances from the planet, 

 so that those which arc here termed the second and fourth, correspond re- 



