[ 243 3 
ihe mode of exigence of ele&ricity, but 
the identity of the principle, we mail pro¬ 
duce arguments of greater weight, and 
thefe may be furnifhed by the confidera- 
tion of fenfationS. 
Let us imagine ourfelves placed upon 
the fummit of a lofty mountain, which 
commands the profpedt of an immenfe 
plain, which prefents us with a world at 
one view. A thoufand different objects 
prefent themfelves at the fame moment, 
and a thoufand different impreffions are 
imade upon the brain in the fame fpace of 
time, although We may not have diftindt 
ideas of all of them. 
A man who has an ear for mufic, hears 
a variety of tones and voices at the fame 
inftant, yet is capable of detecting the 
fmalleft error either in the meafure of time, 
or in the accord of found. 
Let us now alk, by what medium the 
impreffions made upon the retina, and thofe 
R 2 upon 
