CHAPTER IV 



SOME ACCESSORIES AND THEIR USES 



Let the worker of limited means distinctly under- 

 stand that excellent work is assured by the thought- 

 ful use of the equipment already described. Further 

 expenditure on accessories is not imperative, but 

 it may be deemed desirable. I now proceed to 

 describe a few accessories out of the hundred and 

 one advertised that will materially assist the student 

 in his observations. 



We shall first consider a most valuable illuminating 

 accessory, particularly in its use with high powers — 

 the Substage Condenser. As its name implies, it is 

 used to condense or concentrate light upon the 

 object to a greater extent than can be secured by a 

 mirror alone. Condensers are supplied in mounts 

 which slide into the understage collar (see Fig. 5, 9), 

 or can be centred in the focussing substage fitted to 

 higher-priced microscopes. The commonest form 

 is known as the Abbe Illuminator, which costs from 

 about 17s. 6d. upwards, according to additional con- 

 veniences. The better forms are distinguished by 

 larger lenses, the inclusion of an iris diaphragm, 

 and a carrier for the stops used to obtain dark- 

 ground illumination. 



In use, the condenser is first slipped into the 

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