24 
Rainey on Artificial Light. 
Now that which gives the peculiar burnish or glow to all 
objects when highly illuminated, whether by the direct rays of 
the sun, or by light proceeding from ignited matter, is due to 
the heating portion of the spectrum and certain coloured rays. 
In the former case we make use of light for microscopic illu- 
mination which has been deprived of this burnish by its 
having passed through the clouds ; and in the latter this can 
be equally well effected by passing the light emanating from 
gas or a lamp through such transparent coloured media as 
will stop the calorific rays, and at the same time furnish the 
kind and amount of colour necessary to form, with the coloured 
rays of the flame, white light. 
I'he combination which 1 find to answer best is the fol- 
lowing : — 
One piece of dark blue glass, free from any tint of red, one 
of a very pale blue with a slight shade of green, and two of 
thick white plate glass, all cemented together with Canada 
balsam. 
This combination so completely stops the calorific rays, that 
when the direct rays of the sun are concentrated by a bull's 
eye of the ordinary size upon a lucifer-match with this medium 
intervening, it does not become ignited ; and when this medium 
is used with Gillett's condenser, objects illuminated by the 
light of a camphine lamp appear as if they were seen by a 
bright daylight. 
