ll')\V TO WORK 



PART I. 



THE MICROSCOPE AND GENERAL MICROSCOPICAL APPARATUS OF 

 ILLUMINATING OBJECTS OF DRAWING, ENGRAVING, AND MEASUR- 

 ING INSTRUMENTS, GLASS CELLS, CEMENTS, PRESERVATIVE 



FLUIDS, AND OTHER THINGS REQUIRED IN ORDINARY MICRO- 

 SCOPICAL WORK. 



* 



2. The Microscope. It is not desirable in a practical work like the 

 present, to enter into minute details, concerning either the mechanical 

 or special arrangements of the microscope, especially as there are 

 many excellent books published in this country, in America, and on 

 the Continent, in which these points are fully discussed. I shall 

 therefore allude only in general terms, and as briefly as possible, to 

 the various parts of which the microscope is composed. 



S. Simple ami Compound Microscopes. The simple microscope, 

 fig. 2, pi. I, is of use chiefly in the examination and dissection of com- 

 paratively large objects. It consists of a firm support, on which the 

 stage or rest for the object is placed, the mirror being beneath, and 

 the object glass above. In this arrangement the magnified image of 

 the object passes at once to the eye of the observer. 



The compound microscope is the only one now used for micro- 

 scopical research. Until those great improvements in the mode of 

 combining the glasses, now universally adopted, had been introduced 

 by the successful labours of Mr. Lister, Mr. Ross, and others, the 

 compound microscope was a very imperfect instrument, and even up 

 to the present century the simple microscope, as employed by 

 Leeuwenhoek, and improved by Wollaston and others, possessed 

 many advantages over its more complex but imperfect rival. 



In the compound microscope, fig. i, the object is magnified in the 

 first instance by the object-glass^ c, and brought to a focus within the 

 tube, as represented at A, in the diagram. This magnified image 

 is again magnified by the eye-piece, B. The image is of course in- 

 verted, but this inconvenience may be obviated by causing it to 

 pass through another set of lenses inserted in the tube of the micro- 

 scope, and termed the erector. This instrument consists of a tube, at 

 one end of which is a plano-convex lens, and at the other a meniscus, 

 a diaphragm being placed about midway. This is inserted in the tule 



