THE MICROSCOPE AND ITS PARTS. 45 



bination of eye-piece and objective will have a magnify- 

 ing power of ten diameters ; if each y^- inch microm- 

 eter space measures -^ inch, the power will be forty 

 diameters ; each, therefore, corresponds to ten times. If 

 the YoVtf mc h micrometer spaces measure, when drawn, 

 Y 1 ^ inch, then each tenth corresponds to a power of one 

 hundred times ; therefore, if the ^-^ inch spaces, when 

 magnified, measure ten-tenths, the power of that eye- 

 piece and objective is of course one thousand diameters, 

 or ten times one hundred ; if five-tenths, then five times 

 one hundred. 



The owner of a microscope should never take a walk 

 in the country without one or two wide-mouthed bot- 

 tles in his pocket. Empty morphia bottles, to be had 

 of any druggist, are convenient for small collections ; 

 for greater quantities an empty quinine bottle, and for 

 still larger gatherings of aquatic plants the ordinary 

 glass fruit-jar is admirable if a string is added for a han- 

 dle. No bottle should be entirely filled and corked, or 

 all animal life will be animal death before the micro- 

 scope is reached. Leave a large space for air between 

 the cork and the water. 



Those desiring information as to the optical construc- 

 tion of the compound microscope, the uses of the numer- 

 ous pieces of apparatus often used for advanced work, 

 and about the methods of permanently mounting micro- 

 scopic objects, may advantageously consult the follow- 

 ing publications : 



