THE COMPOUND MICROSCOPE. 81 



to the mirror, and is moved with it on the bar, so that 

 the axes of its lenses may coincide with those of the object- 

 glasses. To the stage may be fixed all the usual apparatus, 

 and even a frame of large size for holding such objects as are 

 three or four inches broad. The weight of this instrument is 

 very great, and it is remarkable for its steadiness and the 

 excellence of the workmanship ; its price, with all the appara- 

 tus complete, approaches nearly to one hundred pounds. In 

 consequence of the great amount of labour expended in its 

 construction, and its necessarily high price, the demand for 

 this microscope has not been great for the last few years, the 

 three previously described having in a measure superseded it. 

 Another very useful microscope for general purposes, made by 

 Messrs. Powell and Lealand, is much less costly than any of 

 the others, the tripod and supports for the compound body 

 and stage being made of cast-iron ; the stage is of large size, 

 and they have lately effected a great improvement in it by 

 making it adjustable by a lever ; in the stages hereafter to be 

 described with the lever movement, two or more plates are 

 employed, but in this instrument one only is used, and it per- 

 forms exceedingly well, being very steady even with the 

 highest powers. The compound body is supported on an arm 

 fixed to the back of it, and the coarse adjustment is made by 

 rack and pinion, the fine by a screw acting on the end of a 

 lever. This microscope is available for all the purposes to 

 which the more costly ones are apphed, and is particularly- 

 useful to the medical student, to whom its low price is also a 

 great recommendation. 



MB. boss's COMPOUND AND SIMPLE MICROSCOPE. 



This instrument, first described by Mr. Ross, in the London 

 Physiological Journal, in 1843, is represented by Plate 1 ; and 

 as no language of the author could convey so good an idea of its 

 construction as that given by Mr. Eoss himself, he wiU here 

 take advantage of it, and quote his own words: — 



« The mechanical construction represented in Plate 1, is 

 derived from a practical acquaintance with the various im- 

 6 



