ILLUMINATION. 85 
a certain extent, obviated by the use of a paralleliser, 
but still the light is not much to be recommended. 
Next in order after lime-light is probably acetylene, 
one burner only should be used, but the light is very 
actinic. Messrs. Thorne and Hoddle, of Victoria 
Street, Westminster, make very good acetylene gene¬ 
rators, and Tylar’s “ Dreadnought ” is very handy. 
For the very lowest powers it will be found helpful, 
if not necessary, to use a piece of ground-glass behind 
the substage; this, combined with a parallel beam from 
the radiant, will be found to solve a difficulty which 
often crops up in work with such glasses as the 70 and 
35 mm. glasses of Zeiss. 
For very low power work it has also been found 
useful to adopt as condenser, and to place close up to 
the object, the field glass of a low-power Huyghenian 
ocular, as suggested by Mr. Nelson. 
