88 
Mr. Bennet's Experiments on a new 
vibrations made in the universally diffused caloric or matter 
of heat, or fluid of light. I think modern discoveries, espe- 
cially those of electricity, favour the latter hypothesis. 
EXPERIMENT XL 
When cold wires are introduced within the glass jar, and 
near the light suspended substances, as bits of straw, or very 
fine wires, a very slight motion of the introduced substances 
pushes the suspended wires at the distance of an inch, appear- 
ing like repulsion, but a contrary motion draws them nearer ; 
therefore it may be attributed to the motion of the air. Also, 
when a spider's thread, without any thing attached to it, is 
suspended in a dry glass jar, it recedes from the electric atmo- 
sphere of an excited glass tube brought suddenly near the out- 
side of the glass jar, whether the tube be positively or nega- 
tively electrified ; and when the tube is suddenly removed, the 
thread is drawn after it. This may be accounted for by the dif- 
ficulty with which the spider's thread changes its state of elec- 
tricity, being a very imperfect conductor ; whence also, notwith- 
standing its extreme fineness, it is unfit to be used as an elec- 
trometer. 
EXPERIMENT XII. 
It is indispensibly necessary that a magnetic needle, intended 
for the discovery of minute quantities of magnetic attraction, 
should be inclosed in a proper apparatus, that the motion of 
the air may not disturb it, and that the substances to be tried 
may be brought sufficiently near, and at right angles with the 
point of the needle. The following instrument was con- 
structed for this purpose, and is submitted to the approbation 
