Bauhaus-Universität Weimar

Optical Projection: A Treatise of the Use of the Lantern in Exhibition and Scientific Demonstration
Wright, Lewis
only some of the coarsest can be shown even imperfectly by 
the lime-light, as the stopping down of the light to get crispness 
impairs the brilliancy so seriously. A good \ or £ amplified 
does the best wrork with most of them. 
With polarised light, besides the crystallisations already 
mentioned, all mineral sections which polarise exhibit ex¬ 
cellently ; also fish scales and most organic objects. 
These details, by no means complete, will be sufficient to 
show how wide is the range of the projection microscope 
even with oxy-liydrogen illumination. 
102. Living Objects.—Pond life is always a popular sub¬ 
ject, and the vast mass of objects can be shown with ease 
in the projecting microscope. The larger beetles and larvæ 
are not really microscopic, but require a large trough in the 
ordinary stage of the lantern. For smaller objects a variety 
of glass troughs must be provided, which can be procured 
for Is. each upwards. The troughs should be so thin as 
only to allow the creatures to move freely in the same plane ; 
for free movement they must not be tighter than this. Often, 
for more minute examination, as of the internal organs of a 
water-flea, it is necessary to check the power of movement 
by somewhat compressing the animal. This can be done by 
using a live-box, or by slightly forcing the creature into a 
rather thin trough with the end of a sable pencil, or by 
placing it with a drop of water on one of the glass slips made 
with a concavity on one side, and covering it with a thin 
glass, held on by capillary attraction. Very small animals, such 
as rotifers, are often best dealt with by placing them in a drop 
of water on a plain glass slide, and covering them with a thin 
slip ; or if the pressure would be too great thus managed, 
the creature may be encircled with a bit of cotton thread. 
Glass troughs are very easily made to any thickness, by 
taking an ordinary 8x1 slip, and a thin piece of cover-glass, 
and cementing between them, with dried Canada balsam 
dissolved in benzol, the half of a vulcanised rubber ring. If


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