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teenth century Jansens had made several microscopes, but according 

 to Hogg the first reliable information was with regard to the com- 

 pound microscope of Dr. Hooke in 1667 ; his discoveries were soon 

 followed by those of Divini and Bonnani. From thence up to the 

 present day improvements have successively taken place, and the 

 evolution of the modern microscope has resulted. 



A knowledge of the main principles of the science of optics is 

 necessary for a proper comprehension of the theory of the micro- 

 scope, but it is not within the scope of this paper to more than refer 

 to the fact. 



I would advise the intending microscopist at the outset to obtain 

 a good stand, so constructed that at any future time he might add 

 further necessary apparatus. 



Commencing with the stand, I will describe its various appliances 

 in their proper sequence, bearing in mind that the objective or 

 "object-glass," the eyepiece, and the condenser are of primary 

 importance. Roughly speaking, stands are of two kinds — the pillar 

 and horseshoe foot, and the tripod. Continental makers adopt the 

 former principle, English the latter. The continental form is gene- 

 rally the cheaper but is considered by some workers to be " top- 

 heavy " on account of the unequal distribution of the weight on the 

 pillar, and as the stand should be capable of inclination, this is a 

 disadvantage when used for photographic purposes. In consequence 

 the tripod form of stand is being universally adopted by makers. 



It will be appropriate here to remark that since photography has 

 become so generally applied to the microscope* makers have realised 

 the fact that all their instruments must be constructed with this 

 object in view. 



The " tube" is that portion of the stand which carries the eyepiece 

 and objective, and is made in two patterns — the continental, short 

 and wide, 6 in. (160 mm.), and the English, long and narrow, 10 in. 

 (250 mm.) in length, this latter length being taken as the normal 

 visual distance. The continental pattern is to be preferred, especi- 

 ally for photomicrography, and is the principle upon which all the 

 best English makers now work. On account of the shortness of the 

 tube in the latter, it is necessary that it be fitted with an inner or 

 draw tube, which lengthens from six to ten inches. Its use is for 

 increasing the magnification of the image formed by the objective, 

 and for cover-glass correction. These and the following remarks 

 apply to the monocular microscope, which is the instrument in 

 general use. The binocular is more suitable for viewing opaque 

 objects illuminated by reflected light, and for this purpose is not 

 used, except under special conditions, with higher powers than 

 i-inch. Very beautiful effects are obtained by its use with suitable 

 illumination of such objects as crystals, diatoms, foraminifera, eggs 

 of insects, etc. Having selected the stand, we will turn our attention 

 to that most important part of the microscope, the objective, or 

 object-glass. 



