42 PHOTO-MICROGRAPHS. 
For powers up to one hundred diameters, when 
sunlight reflected from the clear blue sky is em- 
ployed, no condensing lens is required, and the 
beginner is advised to make his first efforts with 
the simple apparatus indicated, using a good one- 
inch objective, and selecting as the object to be 
photographed the cuticle of some plant, such as 
the lily or the house-leek, or a very thin trans- 
verse section of some succulent stem. 
For powers above one hundred diameters, it will 
be advisable to use a condensing lens, and an 
ordinary one-fifth-inch objective will answer the 
purpose very well, when the object-glass used is 
anything below one-eighth-inch. It is best to have 
a little metal cap over the face of the condensing 
lens, with a small aperture in the centre which 
permits the passage of only so much of the light 
as is required for the illumination of the field, 
when the higher powers are used. 
The sub-stage of the microscope should be pro- 
vided with means for focusing the condenser for- 
ward and back. 
A spring nose-piece is required when high 
powers are used. 
A mechanical stage is not essential, even for 
work with the highest powers; but it is a great 
convenience, and one who proposes to do much 
work will scarcely be willing to dispense with it. 
In the absence of a mechanical stage, it is im- 
portant that the hand movement be very smooth 
and steady, as objects often require to be carefully 
centred for photography ; and when a good field 
