the Density of the Earth, yg j 
^ day, I next morning observed the arm, and, having found it 
to be stationary, turned the weights half way round on their 
axes, but could not perceive any motion in the arm. Having 
suffered the weights to remain in this position for about an 
hour, I turned them back into their former position, but without 
its having any effect on the arm. This experiment was re- 
peated on two other days, with the same result. 
We may be sure, therefore, that the effect in question could 
not be pioduced by magnetism in the weights ; for, if it was, 
turning them half round on their axes, would immediately have 
changed their magnetic attraction into repulsion, and have pro- 
duced a motion in the arm. 
As a further proof of this, I took off the leaden weights, and 
in their loom placed two 10-inch magnets; the apparatus for 
turning them round being left as it was, and the magnets be- 
ing placed horizontal, and pointing to the balls, and with their 
north poles turned to the north ; but I could not find that any 
alteration was produced in the place of the arm, by turning' 
them half round, which not only confirms the deduction drawn 
from the former experiment, but also seems to shew, that in 
the experiments with the iron rods, the effect produced could 
not be owing to magnetism. 
T.he next thing which suggested itself to me was, that pos- 
sibly the effect might be owing to a difference of temperature 
between the weights and the case ; for it is evident, that if the 
weights were much warmer than the case, they would warm 
that side which was next to them, and produce a current of air, 
which would make the balls approach nearer to the weights. 
Though I thought it not likely that there should be sufficient 
difference, between the heat of the weights and case, to have 
3 Ra 
