Suspension of the Magnetic Needle. 87 
Cav allots direction, were suspended in a cylindrical glass jar ; 
to the lowest of these rings a spider's thread, three inches 
long, was attached. This thread was fastened to a gold wire 
twisted round the middle of a small sewing needle. The jar 
was placed with its mouth downwards, and over the edge of a 
table, the needle hanging a little lower. After the needle and 
rings of horse-hair were perfectly at rest, the point of the 
needle was struck with the end of my finger, which caused it 
to turn round very swiftly, yet this twisting did not move 
the rings of horse-hair. A11 harpsichord wire, twenty-one 
inches long, was suspended by ten spider's threads, to the 
lowest ring of the horse-hair chain ; this was also frequently 
turned round without moving the rings. A wire of this length 
was afterwards suspended by spider’s threads in a proper frame, 
and with an ivory scale of degrees, with an intention to ob- 
serve the daily variation ; but it was too much influenced by 
heat, which I have not yet been able to obviate. 
EXPERIMENT X. 
To the end of a fine gold wire, three inches long, and sus- 
pended by a spider's thread in a cylindrical glass, was fastened 
a small circular bit of writing paper ; light was admitted 
through a small hole, and also the focus of a large lens was 
thrown upon the paper, with the intention of observing whe- 
ther it would be moved by the impulse of light : but though 
these experiments were often repeated, and once with the 
paper suspended in an exhausted receiver, yet I could not per- 
ceive any motion distinguishable from the effects of heat. 
Perhaps sensible heat and light may not be caused by the in- 
flux or rectilineal projections of fine particles : but by the 
