2 9 1 
the mean density of the earth. 
Here the medium of the first six of these experiments is 
5.19 ; of the other twenty-three experiments it is 5.43 ; and 
the mean of both these means is 5.31, instead of 5.48, as 
stated in the former table, being the error arising from the 
sum of the numerical calculations. The remaining difference, 
0.31, about the 17th part of the whole, must therefore be 
ascribed to the inaccuracy of making and reading off experi- 
ments, with such intricate and inadequate machinery. 
I cannot conclude this paper of enquiry, without expressing a 
hearty wish for the repetition of the large or mountain experi- 
ment, in some other favourable situation, and with improved 
means, if possible. For this purpose, I shall venture just to 
mention an idea which has sometimes occurred to my mind, 
namely, that one of the large pyramids in Egypt might pro- 
fitably be employed, instead of a mountain, for this experi- 
ment. Such a body offers several advantages for the purpose. 
In the first place, the mass is sufficiently large, standing on 
a base of about the size of the whole space of Lincoln's Inn 
Fields, and of a height almost double of that of St. Paul’s 
steeple ; then the station for the plummet, or zenith sector, 
could be taken much nearer the centre of the mass, than on 
a mountain, which would give a larger quantity of deviation 
of the plummet ; then the regular figure and the known 
composition of the mass would yield great facilities in the 
calculation of its attraction ; lastly, the deviation of the 
plummet might be observed on all the four sides. Should 
such a project take place, it will be best to take the stations 
at about one fourth of its altitude above the base, that being 
the place where the deviation of the plummet would be the 
greatest. Finally, so favourable for such an experiment do 
mdcccxxi. P p 
