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CHAPTER III 



MEDIUM-POWER PHOTO-MICROGRAPHY 



In this chapter the camera and its accessories with their suitable means of support 

 are described. 



Inasmuch as the apparatus used in this section, as well as in the next — -critical 

 photography — is the same, we must devote considerable time and space to describe 

 it fully. Primarily it may be said to consist of a microscope with its attendant 

 accessories ; a camera, and an illuminant with the necessary means of support for the 

 whole apparatus. But in this chapter, the camera and its accessories luith their 

 suitable support will alone be considered. 



Inasmuch as the whole requires extreme rigidity, everything must be fixed with 

 the utmost firmness on to a solid table having extra struts between the legs to keep 

 it steady, and the legs themselves should rest on a concrete floor (or anyhow on four 

 concrete supports isolated from the floor), so that any movement on the part of the 

 photographer may not aflect his apparatus. All this preparation for medium-power 

 work may seem superfluous, but as it is an absolute necessity for high-power work, it 

 had better be made carefully from the first. The precautions against tremulations of 

 the floor cannot be too well carried out, and this is the better understood if the reader 

 remembers that when photographing at looo diameters xoVoth of an inch shake in 

 the specimen makes a shift of i inch in the photographic plate. The heat generated 

 by the limelight upon the microscope, too, is not a negligible quantity — for all metals 

 sensibly expand with heat — and in the ai'rangement we use ourselves, to be described 

 later on, is provided against by having a metallic shield to protect the microscope, 

 when we don't use a water-trough, which screen has a hole in its centre only of 

 sufficient size to permit enough light to pass through and fill the substage condenser. 



The tremulations caused by passing vehicles is a source of never-ending trouble to 

 the photo-micrographer, especially if he practises his art in a crowded town, and even 



