SCIENTIFIC SUMMARY. 
363 
Mimas 
12*0 magnitude (Argelander) 
14^ magnitude (Herschel.) 
Enceladus 11*4 
it 
tt 
13 
tt 
tt 
Tethys 
10-5 
ft 
tr 
Ilf 
tt 
tt 
Dione 
10-8 
tt 
ft 
12 
tt 
ft 
Rhea 
9-9 
tt 
tt 
10| 
tt 
tt 
Titan 
8-5 
tt 
tt 
9 
tt 
tt 
Hyperion 13*0 
tt 
tt 
17 
tt 
ft 
Japetus 
10-8 
tt 
tt 
12 
tt 
tt 
Japetus is, however, very variable in "brightness, being at one part of its 
orbit more than three times as bright as at another part. Prof. Pickering 
points out that if this variation in brightness is due to the unequal bright- 
ness of the two hemispheres of the satellite, the satellite must always turn 
the same face to the planet exactly as in the case of our Moon. Mimas 
and Enceladus look fainter than they really are, owing to their proximity to 
the planet. 
Uranus . — The comparative diameters of the two brighter satellites are — 
Titania . . . 586 miles. 
Oberon . . . 544 „ 
The two minor satellites were too faint for measurement. 
Neptune . — The comparative diameter of the satellite of Neptune is — 
Satellite . . . 2260 miles. 
It is thus one of the largest of the secondary members of our solar 
system. 
The suspected Ultra-Neptunian Planet . — No results have been made 
known with respect to the distant planet believed by Prof. George Forbes 
to be at present close to the star (3 Virginis. It is probable, therefore, that 
no attempt has been made to search for this very problematical planet. It 
will be remembered that Prof. Forbes founded his belief in its existence on 
a study of the orbits of the different comets of long period, and that he 
assigned a distance from the Sun of over 100 times that of the Earth, and a 
period of over 1000 years. Prof. Forbes also pointed out, that in 1857 this 
supposed planet would be in the position of the star No. 894 in the Green- 
wich First Seven-Year Catalogue, a star which was only seen in the year 
1857, and on no subsequent occasion. We now learn that this star, No. 894, 
was a tenth-magnitude star, observed by mistake for one of the minor 
planets, and that it still remains in its place. The hypothesis of Prof. 
Forbes that this might be his planet therefore falls to the ground. As 
before pointed out, if Prof. Forbes’s planet really existed, it would probably 
be so faint (like a fourteenth-magnitude star), and would move so slowly 
that it could not be detected without enormous labour with an exceeding 
powerful telescope. 
j Faye's Comet . — This comet was detected by Mr. A. A. Common with the 
37-inch reflector of the Ealing Observatory, on the night of August 2nd, 
very near to the position assigned to it in Dr. Axel Moller’s Ephemeris. The 
comet was very small and faint, so that, although it does not pass its perihe- 
lion passage until January 22nd, 1881, it is probable that it will not be seen 
with any except the few very powerful instruments which are now in 
existence. 
