Royal Astronomical Society. 311 
leaden mass. This point of rest, so called, is not at rest, and 
resembles one of the elements of an elliptic orbit, which would 
remain constant if there were no foreign disturbance, but is per- 
petually changing from the action of other planets. And so fast 
do the indications of the pendulum vary, that is, so rapidly does it 
change the character of its oscillation, even where no visible cause 
is at work, that it cannot be permitted to take a long series of 
observations to determine either the point of rest which precedes 
the change of position of the attracting mass, or that which imme~ 
diately follows. For the instrument is always in a state of change, 
in a manner which would lead to the supposition that the torsion of 
the suspending wire is either visibly influenced by invisible changes 
of temperature, &c., or that it is acted upon by some agent of a 
character wholly unknown. 
From seventeen experiments, Cavendish, in 1797, deduced 5°45 
for the mean density of the earth ; and nothing further was done in 
this species of experiment until 1836, when it was repeated by 
M. Reich of Freiberg, who followed Cavendish’s plan in every par- 
ticular, except in having one leaden mass instead of two. From 
fifty-seven experiments, M. Reich deduced 5:44 for the mean 
density of the earth,—a result almost identical with that of 
Cavendish. 
In the year 1835, the Council of this Society appointed a Com- 
mittee to consider of the best mode of procuring a repetition of the 
experiment. After some delay, occasioned by the difficulty of pro- 
euring funds, and choosing a site, the construction of the necessary 
apparatus was commenced at the end of 1837. On a repre- 
sentation made by the Astronomer Royal, the Government, in the 
year just named, granted 500/. for the purpose; and Mr. Baily 
(to whom the conduct of the whole was intrusted) chose, after 
much deliberation, to make his own house the scene of operation. 
About 400/. has been expended in the actual experiment, and it is 
right here to acknowledge the liberality of the present Govern- 
ment, which has sanctioned the application of 100/. remaining out 
of the sum granted by the late Government, to the payment of part 
of the expense of printing the results. 
I could hardly undertake to make a description of the apparatus 
intelligible in little time, or without diagrams ; but fortunately this 
attempt is rendered unnecessary by the fact of an abstract of Mr. 
Baily’s paper having been for some months in the hands of the 
Fellows of the Society. Keeping in view, then, the main point of 
the present address, I shall make some remarks upon the progress 
of the experiment, with reference to the justification of the decision 
of the Council, on which it will presently be my duty to present a 
gold medal to Mr. Baily. 
And first, with regard to the responsibility which was imposed. 
It ought to be most distinctly understood, that the functions of 
the Committee appointed by the Council ceased as soon as the 
money was obtained for the expenses, and Mr. Baily’s offer of 
