12 THE MICROSCOPE. 



reflector, for drawing the outlines of the magnified 

 images, or for measuring the objects. The camera 

 lucida is a four-sided glass prism, set in a brass frame 

 with a short tube. It is used in this way : you must 

 take off the cap of the eye-piece, and slip the tube of 

 the camera upon the top of the eye-piece ; arrange the 

 microscope in a horizontal position, and look through 

 the camera at a sheet of paper on the table on 

 which you are working ; the magnified image of the 

 object on the stage of the microscope will appear as 

 if it were on the paper below. With a finely-pointed 

 pencil you then proceed to take its outline; do not 

 be disappointed if you cannot see both the image and 

 the pencil ; persevere, and in a short time you will 

 succeed in making your drawing. The neutral tint 

 glass reflector, which is cheaper than the camera lucida, 

 consists of a small piece of slightly coloured glass 

 which fits on the top of the eye-piece ; the micro- 

 scope must be inclined, as before. With a little 

 practice the draughtsman will be able to draw the out- 

 lines on the paper. 



The polarising apparatus, by means of \vhich 

 various splendid colours are made to appear, is a 

 luxury which the beginner may readily dispense with ; 

 though the effects produced, especially when a thin 

 plate of selenite is interposed between the analyser 

 and polariser, are often extremely beautiful ; and 

 though no doubt in some cases the internal structure 

 of transparent objects is rendered very evident, yet 

 for general microscopic work the polarising apparatus 

 is not necessary. 



Various lamps have been suggested as convenient 

 forms for illumination. I do not think you need 

 trouble yourself about a choice ; a moderator or 

 paraffin will serve your purpose well ; only take care to 

 use a lamp, and not candles, the constant flickering 



