Royal Astronomical Society. 305 
The President (Lord Wrottesley) then addressed the Meeting on 
the subject of the anard of the Medal, as follows :— 
Gentlemen,—I have now the gratifying duty of stating to this 
meeting the grounds on which the Council have thought it right to 
award a Gold Medal to Mr. Francis Baily for his experiments to 
determine the mean density of the earth, in repetition of what is 
generally termed the Cavendish Experiment*. In the performance 
of this duty, I am necessarily required to offer a few remarks on 
the nature and utility of the end sought, on the previous attempts 
which had been made to gain it, and on the manner in which the 
one now before us was conducted by the distinguished friend of the 
Society to whom we are this day to offer our highest token of 
acknowledgement. 
The labours of the astronomer are directed not only to the 
accurate determination of the motions of the heavenly bodies, but 
also to that of their constitution and organization. If the papers 
in our Memoirs and those of other kindred societies seem to 
dwell much upon the former division of the subject, and little upon 
the latter, it is not of preference, but of necessity. Our means of 
determining satisfactorily anything which relates to the constitu- 
tion, even of the bodies of our own system, are few and limited ; 
while those which apply to the prediction of their relative motions 
constitute the most perfect body of science which exists. But all 
which is known, certainly or conjecturally, of the interior arrange- 
ments of the heavenly bodies, is of the highest interest, and most 
especially when its action upon the minds of men is considered. 
Those who have heard the son and successor of the patriarch of this 
branch of astronomy, on occasions similar to the present one, de- 
liver his views upon the general constitution of planetary systems, 
cannot but have felt that the subject which could inspire such 
thoughts must, were it for that reason only, be among the noblest 
to which human energy can be directed. 
The masses of the planetary bodies are important data of the 
Newtonian theory of gravitation, but only in a relative sense. If, 
at any given instant, each one of the innumerable particles of which 
the universe is composed were to acquire a doubly attractive power, 
and, at the same moment, a double resistance to the alteration of 
its state, the effect of the change would be unseen and unfelt, so 
far as the motions of the system are concerned. Nothing, there- 
fore, is needed, in this last point of view, except a knowledge of 
the relative quantities of matter contained in the different planets. 
There is something vague at the outset in the term mass or 
quantity of matter. With this the calculator of the planatary 
motions has nothing to do: the term mass is to him merely a 
convenient name for the numerator of the fraction which expresses 
the attractive force of that planet; and what number stands in any 
one numerator is of no consequence whatever, provided that all 
* See Phil. Mag. S. 3. vol. xxi. p. 111. 
Phil. Mag. 8, 3. Vol. 22. No. 145, April 1843. X 
