the Density of the Earth. 521 
From this table it appears, that though the experiments agree 
pretty well together, yet the difference between them, both in 
the quantity of motion of the arm and in the time of vibration, 
is greater than can proceed merely from the error of observa- 
tion. As to the difference in the motion of the arm, it may 
very well be accounted for, from the current of air produced 
by the difference of temperature ; but, whether this can account 
for the difference in the time of vibration, is doubtful. If the 
current of air was regular, and of the same swiftness in all parts 
of the vibration of the ball, I think it could not ; but, as there 
will most likely be much irregularity in the current, it may very 
likely be sufficient to account for the difference. 
By a mean of the experiments made with the wire first used, 
the density of the earth comes out 5,4,8 times greater than that 
of water; and by a mean of those made with the latter wire, it 
comes out the same; and the extreme difference of the results of 
the 23 observations made with this wire, is only ,75 ; so that 
the extreme results do not differ from the mean by more than 
,38, or 1 I T of the whole, and therefore the density should seem 
to be determined hereby, to great exactness. It, indeed, may 
be objected, that as the result appears to be influenced by the 
current of air, or some other cause, the laws of which we are 
not well acquainted with, this cause may perhaps act always, 
or commonly, in the same direction, and thereby make a con- 
siderable error in the result. But yet, as the experiments were 
tried in various weathers, and with considerable variety in the 
difference of temperature of the weights and air, and with the 
arm resting at different distances from the sides of the case, 
it seems very unlikely that this cause should act so uniformly 
in the same way, as to make the error of the mean result nearly 
MDCCXCVII I. 3 X 
