279 
the mean density of the earth. 
other necessary measures, gave a final result of 11.6 seconds, 
for the sum of the deviations of the plumb line, on both sides 
of the mountain ; and that, in all probability, within much 
less than half a second of the truth. Other instruments used, 
were the Royal Society's transit instrument made by Mr. 
Bird, and an astronomical clock by Shelton, which had 
both been provided on occasion of the observations on the 
transit of Venus, in 1761 or 1769. Besides these and several 
other instruments, one of Ramsden's best theodolites was 
used, in measuring the figure and dimensions of the moun- 
tain, which was performed in the most correct manner by 
skilful surveyors ; so as that thence an exact model of it 
might be made, or all its dimensions accurately taken, for 
computing the attraction. 
By only reading over the accounts of these operations, (in 
the places before mentioned ) made by means of such instru- 
ments, and in such hands, every person must be convinced of 
the impossibility that any error could have been committed, 
capable of causing any sensible inaccuracy in the conclusion 
of the work. 
It remains now to describe the share which I bore in this 
important business ; which consisted in taking all the mea- 
surements as above described, and from those data, calcu- 
lating what must have been the exact magnitude of the 
mountain ; what its attraction on the plummet, relatively to 
that of the globe of the earth on the same ; and what must 
be the mean density of the earth. These computations, 
which employed my daily and assiduous labours during the 
greater part of two years, are recorded in the Philosophical 
Transactions of the year 1778, and also in the second volume 
