4 On the Mean Density of the Earth. 
opinion is promptly assumed that the latter small experiment is 
susceptible of the greater accuracy, and the numbers in its result 
gratuitously adopted as nearer the truth than that of the former. 
As this is an opinion which I have never been able to bring my 
mind to acknowledge ; and as it is a matter of great importance 
in the present state of physics, I have been desirous to draw the 
attention of philosophers to a closer consideration of the subject ; 
with a view to a more deliberate and impartial decision of this 
point. 
From the closest and most scrupulous attention I can employ 
on this question, the preference, in point of accuracy, appears 
to be decidedly in favour of the large or mountain experiment, 
over that of the small balls. It is indeed true, that though the 
large mass of the mountain must yield an immensely greater force 
than a small ball; yet it may he said that this advantage must be 
balanced, either wholly or in great part, on the score of distance, 
as the plummet is acted on at a great distance from the centre 
of the mountain, while the balls are approached very near to- 
gether; so that the visible effects may thus be nearly equal, by 
the'reciprocal balancing between magnitude and distance. Hence 
the visible effect of the mountain, is that of the small angle of 
11 or 12 seconds, by which the plummet is drawn aside from the 
perpendicular; thereby showing that the attraction of the earth, 
on the plummet, is to that of the mountain on it, as radius is to the 
tangent of those seconds; while, in the other experiment, the 
small pendulous balls are drawn aside by the large ones the space 
of between + and # of an inch; the distance of each ball from the 
middle of their connecting rod being a little more than 36 inches. 
The first or immediate small results of the two experiments, thus 
appearing so far to be about equally favourable, it will be necessary 
to examine the circumstances of each of them separately, that 
we may be able to judge more particularly of their merits; and 
first, of the Schihallien experiment. 
This experiment, it is well known, was conducted by the late 
astronomer royal, Dr. Maskelyne, than whom a more correct, 
faithful and experienced individual probably never existed. The 
accounts of his measures and observations, taken in conducting 
it, are minutely detailed in the Philosophical Transactions of the 
year 1775, or in my edition of the Transactions, vol. xiii. p. 702; 
where all the instruments and operations are particularly de- 
scribed in the most plain and satisfactory manner. The principal 
instrument was the ten-foot zenith sector; with which the me- 
ridian zenith distances of 43 stars, by 337 observations, were 
carefully taken, both on the north and south sides of the moun- 
tain. The medium of all these, with other necessary measures, 
gave a final result of 11-6 seconds, for the sum of the igeee 
ce) 
