MICROSCOPICAL APPARATUS. AT 
The oil of cedar, which was first introduced 
for use with the latter, has generally been aban- 
doned, because of its solvent action on cements, 
and a viscid fluid has taken its place, consist- 
ing of some salt dissolved in glycerine, to ob- 
tain the proper refractive index. This viscid 
fluid causes the thin glass cover to adhere so 
strongly to the front lens of the objective, that the 
cover itself, if not fastened by cement, or even the 
whole slide, is lifted when the attempt is made to 
focus upon the object. For this reason, dry or 
water-immersion lenses are more convenient for 
every-day use. 
When working with a heliostat, an amplifier may 
be used in the tube, to increase the magnifying 
power. With a first-class amplifier, such as that 
manufactured for this purpose by Tolles, of Bos- 
ton, the amplification is nearly doubled, without 
any marked loss of definition. The amplifier must 
be adjusted by means of the draw-tube with refer- 
ence to the distance of the screen and the power 
of the objective. 
1 Hydrate of chloral dissolved in glycerine is perhaps the favor- 
ite immersion fluid. 
