MICROSCOPICAL APPARATUS. 41 
evident that the light is greatly attenuated, and 
the time of exposure must be correspondingly 
long. If we suppose that the illumination would 
be sufficient to photograph the object in one 
second of time at its natural size, then the time 
required when it is magnified twenty-five diame- 
ters should be the square of twenty-five, or 625 
seconds. As a matter of fact, the time required is 
considerably more than this, and some more effi- 
cient mode of illumination is required. 
One plan which has suggested itself is to con- 
centrate the light from a larger area upon the 
Lieberkiihn by means of a metal or glass funnel 
silvered upon the inside. 
Or artificial illumination might be employed by 
means of a platinum wire made incandescent by a 
powerful electric current, and arranged in a circle 
just behind the lower end of the objective in such 
a manner that the light would fall upon the ob- 
ject, and that only reflected light could enter the 
objective. A Lieberkiihn behind the incandes- 
cent wire would be required as a reflector. It will 
be understood that these are merely suggestions 
which have not been put to the practical test. 
II. MICROSCOPICAL APPARATUS. 
ALL that is absolutely required in the way of 
microscopical apparatus in order to make a com- 
mencement, is a monocular stand of the simplest 
construction and a low-power objective. 
