Dr. Wentworth Eron on the Satellites of Mars. 37 
A=Diameter of planet. 
D=Distance from us. 
V=Radius vector, or distance from Sun. 
N=Comparative reflecting power of surface. 
Calculated according to this formula, and assuming equal reflection, the apparent 
brightness would have been on 5th Nov., Jupiter 100; Mars 260; Saturn 8.6, and 
Vesta 0.034, whereas the actual brightness was—Jupiter 100; Mars 90; Saturn 9, 
and Vesta 0.040. 
These figures evidently agree as well as could be expected, except in the case of 
Mars, whose light ought to have been three times as great as it was; whence we 
infer that his surface reflects only one-third of the light reflected by the other 
planets, and thus the foregoing direct comparison with Vesta receives additional 
confirmation. 
So. then the diameter of the Satellite, obtained from direct comparison 
with Mars is 14 miles: from comparison with Vesta 13.2 miles, giving 
a mean diameter of 13.6 miles, or 3} 5th part of that of Mars himself, corresponding 
to a disc, at the mean distance of Mars, of about ,4,th of a second are. 
If the diameter of the satellite be , oth, its volume will be 37 5,5,955, and the 
mass probably about zo5900,006 Of that of Mars. 
Two such satellites as these, at the respective distances of 2.7 and 6.8 radii, 
would be utterly powerless to produce any sensible tidal action on the seas of Mars. 
The preceding observations refer to the outer satellite ; the inner one has been 
repeatedly observed in America, viz., at Harvard College and at Glasgow, Missouri, 
as well as at Washington; but it has not been seen, with certainty, so far as I 
know, in Europe. , 
The planets of our system, commencing with the Earth are now shown to be 
accompanied by satellites whose numbers are in geometrical progression : thus, the 
Earth has 1, Mars has 2, Jupiter has 4, Saturn has 8, Uranus has, at least 4, and 
probably a greater number, while the exceeding great distance of N eptune 
prevents us from recognising more than one of his. 
Probably it was the single step wanting in this progression which suggested to 
Swift and Voltaire their guesses as to satellites whose existence has now, for the 
first time, been ascertained, 
