THE MICROSCOPE AND ITS PARTS. 43 



that combination of eye-piece and objective will have 

 a magnifying power of ten diameters; if each y^ inch 

 micrometer-space measures ^ inch, the power will be 

 forty diameters; each, therefore, corresponds to ten 

 times. If the yoVb- inch micrometer-spaces measure, 

 when drawn,. ^ inch, then each tenth corresponds to 

 a power of one hundred times; therefore, if the y^jVo- 

 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 

 handle. No bottle should be entirely filled and 

 corked, or all animal life will be animal death before 

 the microscope 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 seen for advanced work, 

 and about the methods of permanently mounting mi- 

 croscopic objects, may advantageously consult the fol- 

 lowing publications: "How to Use the Microscope," by 

 John Phin; i6nio.. New York.— "How to See with the 

 Microscope," by Dr. J. E. Smith; i2mo., Chicago. — 

 "How to Work with the Microscope," by Dr. Lionel S. 

 Beale; 8vo., London.— Carpenter's "The Microscope 

 and its Revelations," edited by Dallinger; 9th edition. 



