[ 7 8 4 1 
four minutes. Then will the'air be found to be ne- 
gatively cledrical ; and will continue fo a confider- 
able time after the apparatus is removed into another 
room. 
The air without-doors I have fometimes known 
to be eledrical in clear weather; but never at night, 
except when there has appeared an aurora borealis, 
and then but to a fmall degree, which I have had 
leveral opportunities of obferving this year. IIow 
far pofitive and negative eledricity in the air, with 
a proper quantity of moifture between, to ferve as a 
condudor, will account for this, and other meteors 
fometimes feen in a ferene iky, 1 fhall leave to the 
curious in this part of natural pbilofophy to deter- 
mine. That dry air at a great diflance from the 
earth, if in an eledric date, will continue fo till it 
meets with inch a condudor, fcems probable from 
this experiment : An excited glafs tube with its na- 
tural polifh, being placed upright in the middle of a 
room, by putting one end of it in a hole made for 
that purpofe in a block of wood, will generally lofe 
its eledricity in lefs than five minutes, by attrading 
to it a fufficient quantity of moifture, to condud the 
cledric fluid from all parts of its furface to the floor. 
But if, immediately after it is excited, it be placed 
in the fame manner before a good fire, at the diflance 
of about two feet, where no moifture will adhere to 
its far face, it will continue cledrical a whole day; 
and how much longer 1 know not. It may not be 
improper to mention here, that if a folid cylinder of 
glafs be fet before the fire till quite dry, it may as eafily 
he excited as a glafs tube, and will ad like one in 
every 
