5 i 8 Mr. henly’s Experiment's ami 
coating on a and b (after laying them again together as 
at firft) were touched, at the fame time, by a thumb and 
finger of the hand, or any conductor communicating 
with the earth, the plates would then, on being leparated 
(the experiment being made in a dark room) emit a ltrong. 
flafh. of light ; and this phenomenon Mr. lane has fre- 
quently produced twelve or fourteen times fucceliively,. 
touching the coating of the plates each time before the 
reparation, without renewing the charge in the glafs by 
the machine; but if he omitted to touch the coatings as 
above mentioned, no light was viiible on the reparation 
of the plates (}). Should tliofe gentlemen, if any Inch re- 
main, who are of opinion,, that in eledfrical experiments 
two fluids, the vitreous and the relinous, are concerned, 
proceed do make experiments of this kind, they may, 
perhaps, from forne phenomena, be induced to draw 
conclufions which they may think not unfavourable to. 
their own hypothesis. 
My experiments with the excited plate of glafs, pub- 
li filed in the Philofophical Tranfadtions, as before men- 
tioned, may ferve, however, as a key to explain both Mr. 
( b ) Crown-glafs, that is, the glafs commonly ufetl for fafh- windows, though 
fo much thinner, iucceeds in this experiment as well as the plate-glafs ; but what, 
is very remarkable, the Dutch plates, when treated in the fame manner, have 
each a pofitive and a negative furface, and the ele£lricity of both fur.faces, of 
both plates, is exchanged for the contrary eleflricity in the difeharge. If a 
clean, dry, uncoatcd plate of looking-glafs be placed between the coated looking - 
glafs plates, or between the plates of crown-glafs, it appears, after charging, to 
be negatively elcttrified on both Tides; hut if it be placed between the Dutch 
plates, it acquires, like them, a pofitive electricity on one furface, and a negative 
eledricity on the other. Further particulars, with a defeription of fomc new 
elcCtrical apparatus, conflruflcd on account of thefe phenomena, will be given 
at another opportunity. 
f> 
n n t? v ’c 
