2B3 
the mean density of the earth. 
accuracy of the computations made from them. But if any 
such person attentively read over Dr. Maskelyne’s account 
of the measurements, in the Philosophical Transactions of 
1775, his doubts must be soon removed, as to the data sup- 
plied by the survey of the hill, or by the astronomical obser- 
vations. And as to the accuracy of my own computations, 
made from those data, they are fully and fairly before the 
public, in the works before mentioned ; and let any person, 
who doubts, look over and repeat the calculations there stated, 
and try if he can find any inaccuracy in them. The only 
possible ground of doubt in the measured data, must be in 
the observed deviation in the plumb line, taken by Dr. Mas- 
kelyne ; but when we consider the accuracy of the observer, 
and of the instruments, and read the account of the use of 
them, it must be then very difficult to doubt of their accuracy. 
On this point it is commonly acknowledged that a good ob- 
server, with the best instruments, can observe angles to a 
small fraction of a second. Dr. Maskelyne's observations 
give 11.6 seconds for the sum of the deviations of the plumb 
line, from a medium of between 300 and 400 observations. 
Now let us suppose it possible to have committed an error of 
four tenths of a second in this number, and that the true num~ 
ber should have been 12 seconds, instead of 11. 6, being an error 
of the twenty-ninth part of the whole. This then would cause 
an error of the 29th part of the result ; which would reduce 
the density 5 to about 4.8 ; showing that the number 11.6 is 
not too small, but may be the contrary. Next, let us assume 
11 seconds only, omitting the six-tenths, being almost the 
twentieth part of the whole, and which therefore would give 
nearly 5.25 for the earth's density, being still far below the 
mdcccxxi. O o 
