497 
the Density of the Earth. 
moving the weights, fell to the ground, so as not to be in the 
way. On moving the weights to the negative position, they 
were found to be about 8° colder than the air, and their effect 
on the arm seemed now to diminish on standing, instead of in- 
creasing, as it did before ; as the arm was drawn aside about 
2 -|- divisions less, at the end of an hour after the motion of the 
weights, than it was at first. 
It seems sufficiently proved, therefore, that the effect in ques- 
tion is produced, as above explained, by the difference of tem- 
perature between the weights and case ; for, in the 6th, 8th, 
and qth experiments, in which the weights were not much 
warmer than the case, their effect increased but little on stand- 
ing; whereas, it increased much, when they were much warmer 
than the case, and decreased much, when they were much 
cooler. 
It must be observed, that in this apparatus, the box in 
which the balls play is pretty deep, and the balls hang near 
the bottom of it, which makes the effect of the current of air 
more sensible than it would otherwise be, and is a defect 
which I intend to rectify in some future experiments. 
Experiment ix. April 2 q. 
Weights in positive position. 
Extreme 
points. 
Divisions. 
Time. 
Point of 
rest. 
Time of middle 
of vibration. 
h < n 
h > it 
34 ,7 
35 
34 $5 
- 
- ~ 
34^4 
MDCCXCVIII. 
3 s 
