XV 
the t weakeft Natural or Artificial Electricity. 
other, fhould find fome refinance or oppofition in either of 
the fur faces, as will be made more evident in the fecond part. 
It is immaterial whether the non- conducting or femi- conducting 
ft rat um be laid upon one or the other of the planes, it being- 
only neceflary that they fhould coincide very well together, 
which cannot be eafily obtained when a common table is ufed 
for one of the planes, which is the only reafon why it is better 
to ufe two planes which have been worked flat by grinding one 
upon the other, and one of them varnifhed, &c. A Angle 
metal plate, covered with filk, with three lilk firings faftened 
to it by way of a handle, may be conveniently ufed for 
ordinary experiments. 
23. Hitherto we have confidered the ufe of our condenfer in 
exploring the weak atmofpherical eleCtrieity, which is brought 
down by the atmofpherical conductor But this, though 
the principal, is not the only ufe to which it may be 
applied. It ferves likewife to difcover the artificial eleCtrieity 
when this is fo weak as not to be difcoverable by any other 
means, which happens in various cales, fome of which I fhall 
now proceed to mention. 
24. A Leyden phial charged, and then difeharged by touch- 
ing its coated fides three or four times with the dilcharging 
rod, or the hand, feems to be quite deprived of eleCtrieity, yet 
* Here it will be proper to mention a remarkable obfervation, which I have 
made on the atmofpherical electricity with the help of the condenfer. The late 
Mr. canton and others affirmed that they had obtained ftronger figns of eledricity 
from their atmofpherical apparatus at the time of an aurora borealis , than at other 
times ; but various other philofophers doubted of the influence of electricity 
in that meteor, and fome abfolutely denied it. I myfelf was much in doubt 
about it ; but at prefent Mr. canton’s afiertion feems to be eftablifhed beyond a 
doubt, as Ihave obferved by aftual experiment. During the ftrong aurora borealis, 
which appeared in the night of the :8th of July, 1780, the light of which rifing gra- 
dually from the horizon, reached the zenith at near eleven o’clock, and enlightened 
the heavens with a reddifh light, the weather being clear and windy; our con- 
denfing apparatus being applied to an atmofpherical conductor, gave fine bright 
fparks ; whereas, at other times, that is, in clear weather, and at every hour of 
the day or night, the fame apparatus afforded either no fparks at all, or ex- 
ceedingly fmall ones, the reafon of which was becaufe the laid conductor was not 
much elevated. 
