USE OF THE MICROSCOPE 9 



fly's wing with the concave and convex sides of the mirror ? 

 Which side throws more light on the object ? 



G. DIAPHRAGM. Note the circular, revolving disk be- 

 neath the stage with its various sized openings. This disk 

 is called the diaphragm. Try each opening successively, 

 and note the effect on the wing. Which opening is best 

 to use on a dark day ? Which is best to use on a sunny 

 day ? It is best for the eye not to use too bright light. 



H. FOCUSING WITH THE DIFFERENT OBJECTIVES. Using 

 a f objective, run the tube down until the bottom of 

 the objective is about \ inch from the object. With the 

 eye at the eyepiece very slowly lower the tube until the 

 wing comes plainly into view. The object is then said to 

 be in focus. If in lowering the tube the wing is not seen 

 very soon, look at the end of the objective, and note how 

 close it is to the object. If it is nearer than J of an inch, 

 elevate the tube and try again. Watch closely and never 

 run the objective into the object. A f objective will stand 

 about J of an inch from the object when in focus. A J will 

 allow a piece of ordinary paper between it and the object. 



Using the J objective, run the tube down until the end 

 almost touches the object. Then, with the eye at the 

 eyepiece, run the tube up and down with the fine adjust- 

 ment until the wing comes into focus. Always use the 

 fine adjustment with the J objective. 



Mount various objects on slides in water under cover 

 glasses. Cotton fibers, hairs, blood cells, pond scums, etc., 

 will serve for this purpose. Focus with both objectives 

 on these objects again and again, until the operation of 

 lighting and focusing is thoroughly mastered. 



Reference Book. The Microscope and Microscopical Methods 

 by Simon Henry Gage, Comstock Pub. Co., Ithaca, N.Y., $1.50. 



