electrical phenomena exhibited in vacuo. 71 
I made some comparative experiments to ascertain whether 
below the freezing point of water, the diminution of the tem- 
perature of the torricellian vacuum diminished its power of 
transmitting electricit}', or of being rendered luminous by it. 
To about 20 0 this appeared to be the case ; but between 20° 
above and 20° degrees below zero, the lowest temperature I 
could produce by pounded ice and muriate of lime, it seemed 
stationary ; and as well as I could determine, the electrical 
phenomena were nearly of the same intensity as those pro- 
duced in the vacuum above tin. 
Unless the electrical machine was very active, no light was 
visible during the transmission of the electricity; but that 
this transmission took place, was evident from the luminous 
appearance of the rarefied air in the other parts of the syphon, 
and from the diminution of the repulsion of the ball of the 
quadrant electrometer attached to the prime conductor. When 
the machine was in great activity, there was a pale phospho- 
rescent light above, and a spark on the mercury below, and 
brilliant light in the common vacuum. A Leyden jar weakly 
charged could not be made to transmit its electricity by 
explosion through the cooled torricellian vacuum, but this 
electricity was slowly dissipated through it ; and when strongly 
charged, the spark passed through nearly as much space as 
in common air, and with a light visible in the shade. At all 
temperatures below 200°, the mercurial vacuum was a much 
worse conductor than highly rarefied air : and when the 
tube containing it was included in the exhausted receiver, 
its temperature being about 50°, the spark passed through 
a distance six times greater in the Boylean than in the mer- 
curial vacuum. 
It is evident from these general results that the light (and 
