OF GASES, ETC. 41 
to the electric light, though it is probable such 
does exist. 
In the above experiment, when other gases are 
mixed with the rarefied oxygen, the effect is some- 
what increased, probably because a certain amount 
of chemical action is set up. 
Our readers know, that by passing the dis- 
charges of a Ruhmkorff’s imduction apparatus 
through a glass globe in which the air has been 
highly rarefied, a beautiful luminous phenomenon 
occurs and persists as long as the duction ap- 
paratus continues to work. When the vapour of 
some volatile substance, such as alcohol, essence 
of turpentine, naphtha, bichloride of tin, etc., is 
mixed with the air in the glass globe, and a va- 
cuum then produced by the pneumatic machine, 
the luminous phenomenon is still more beautiful. 
The hght forms a series of concentric arches 
separated by dark stratifications; its colour and 
form remind us of the Aurora Borealis; and, in- 
deed, some have looked upon this experiment as 
the production of an artificial aurora, the vacuum 
of the glass globe (which is never a perfect void) 
representing the rarefied air in the higher regions 
of the atmosphere, where the Aurora Borealis 
occurs. 
The lght thus produced, to be seen to advan- 
tage, must be viewed in a dark room, but it is 
faintly visible in full daylight. 
