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CHAPTER IV 



THE MICROSCOPE, LENSES, AND EYE-PIECES USED IN MEDIUM 



AND HIGH-POWER WORK 



In this chapter are explained : Section I. — (i) The microscope stand itself; (ii) the 

 fine adjustment ; (iii) the movable nose-piece and Davis diaphragm ; (iv) the 

 mechanical stage ; (v) the movable substage. 



Section 11. — (i) The objectives ; (ii) numerical aperture, what is meant by the term, 

 and how it is obtained by the Apertometer and by other means ; (iii) eye-pieces. 



SECTION I.— THE MICROSCOPE AND ITS FITTINGS 



(i) The instrument must be one of the best manufacture, for when dealing with 

 high-powers and critical work nothing short of the best will enable the operator to 

 turn out good work. The leading points to bear in mind when choosing a microscope 

 for this work may be summarised under the following six heads : 



I. The Stand Itself. — Must be very heavy, built without shake and ivell 

 balanced when placed horizontally. 



Its base should be broad and its adjustments within easy reach. The general 

 design is much the same as sold by different makers, but the details vary consider- 

 ably, and as these conform to make the superiority or otherwise of the model, so we 

 give blocks of most of the leading firms for comparison. Space will not allow a 

 description of each, and as to the best firm it is purely a matter of taste. All are 

 excellent and the best firms all turn out good work if a proper price be paid. But if 

 the tyro expects to get all that is refined and elegant for the delicate work of photo- 

 micrography for a mere song, or who, neglecting the recognised channels we are 

 pointing out for obtaining trustworthy work, goes haphazard to the nearest " Stores," 

 or to some second-hand tool-shop, he must not expect to be otherwise than disappointed. 



We here append woodcuts of the microscopes sold by many leading manufacturers 

 arranged in alphabetical order, commencing first with the "Nelson" model as made 

 by Baker of Holborn (Fig. 28). We do not propose to occupy time and space by 

 describing each variety, for, seeing this book is only for the assistance of the photo- 

 micrographer and not a treatise on the microscope proper, it would be foreign to the 

 object of the work. 



