46 
Proceedings of Royal Society of Edinburgh. [sess. 
volts. After some minutes, generally till the potential of the 
metal fell to 2000 volts, the non-conducting plate was removed and 
placed, as shown in fig. 4, above the metal plate C attached to the 
quadrant electrometer, and the deflection was observed. For a 
thin piece of glass (0*3 cm. thick) the whole effect of the two sides 
was negative when the electrified metal point or disc had been 
charged positively and vice versa. But on putting two plates of 
glass above the electrified metal, we found the top plate to be 
oppositely charged ; and the under plate to be charged similarly to 
the point or disc, but not so highly. We found corresponding 
results with a plate of paraffin 0'75 cm. thick, and with two plates 
of paraffin, 0*5 cm. and 0'75 cm. thick. When a plate of paraffin 
3 ’25 cms. thick was used, we always found the top face charged 
oppositely to the charge of the metal, whether disc or needle-point, 
and the under face charged similarly to the metal below. Thus 
the apparent total charge of the two faces of a thin non-conducting 
plate is due to the fact that the face of the plate away from the 
electrified metal is more highly charged oppositely than the face 
next the metal is charged similarly. 
Fig. 4. 
