84 Dr. Thomsows Account of the . ae. 
general retain it for a long time ; except glass, which from its 
property of attracting moisture, is speedily deprived of any 
charge that may be communicated to it. Hence the plate of 
tesin of the electrophorus, when once excited, retains its charge 
for a long time, and does not communicate any of it to the metal 
plate, though laid upon it. When a conductor is brought into 
the vicinity of an excited electric, the side of it next the electrie 
acquires the opposite kind of electricity of that of the electric, 
and the furthest off side becomes in the same state as, the 
electric. Suppose the cake of resin charged positively, the side 
of the metal plate next the resin will become negative, and the 
Opposite side positive ; because the electricity of the resin repels 
the electricity of the metal, and drives it to the side furthest from 
itself. If we now touch the side of the metal plate furthest 
from the resin, it will discharge its surplus electricity into our 
body. When the plate is removed from the resin, the electrical 
fluid will spread itself equably through it; but as it has parted 
with a portion of its electricity to our body, it must contain less 
than its usual portion, and of course be negative. A conductor 
brought into its neighbourhood will of consequence transmit a 
spark to it, and restore the usual quantity of electricity to the 
metallic plate. This experiment may be repeated at pleasure, 
because the cake of resin merely alters the distribution of the 
electricity of the plate. Our touching the plate takes away or 
communicates a quantity of electricity, according to circum- 
stances. Hence, when removed, it is constantly excited, and in 
a condition to give out or receive a spark. 
Such is Dr. Ingenhousz’s explanation of the electrophorus. 
I rather think that the first of the principles upon which this 
explanation is founded was new ; at least [ am not aware of any 
person who advanced it explicitly before our philosopher. But 
the second principle was not new, having been advanced by Dr. 
Franklin, and mathematically explained by Mr. Cavendish and 
Epinus. Dr. Ingenhousz does not seem to have possessed 
mathematical knowledge, and, therefore, was not likely to have 
perused the theory of electricity as given by Cavendish imhis 
celebrated paper on that subject, or by Epinus in his well-known 
work ; but it is not at all likely that he was ignorant of the 
‘principles advanced by Dr. Franklin. Accordingly Dr. Ingen- 
housz does not claim the second principle as a discovery of his 
own. He merely makes use of it to show that the phenomena 
of the electrophorus were not inconsistent with the Franklinian 
theory, but really followed from that theory. 
5. Account of a new Kind of Inflammable Air, or Gas, which 
can be made ina Moment without Apparatus, and is as fit for 
Explosion as other Inflammable Gases in Use for that Purpose; , 
with a new Theory of Gunpowder. Phil. Trans. 1779, p. 376.— 
This paper merely makes us acquainted with the fact that ether 
explodes when the vapour of it is mixed with common air, or 
