MAGNIFYING POWER. 17 



lamp when used. It should be applied while hot, 

 with a hair pencil ; and cools very quickly. 



The preservative liquids should be kept in corked 

 bottles, a hair pencil being fixed into the under part 

 of the cork ; or, what is better, in stoppered bottles, 

 the stopper being prolonged to a point nearly reach- 

 ing the bottom of the bottle. 



As soon as the preparations are mounted, they 

 should be labelled, the labels being kept ready gum- 

 med. The balsam should be kept in a capped bottle, 

 such as is used for holding solutions of gum, with an 

 iron wire for removing portions as required. By 

 keeping, the balsam becomes thicker; it may be 

 thinned by the addition of oil of turpentine, and the 

 application of a gentle heat. 



The black japan, &c., may be procured at any oil- 

 shop; the glass rings, cell-sides, covers, &c., from 

 Mr. Norman, 178 City Road, or of the microscope- 

 makers. 



Mounted objects should be kept in shallow drawers, 

 and be laid flat not standing on edge. 



Magnifying power. Before entering upon the con- 

 sideration of the objects themselves, a word or two 

 must be said upon the magnifying powers. In the 

 plates of this work, the serial number of each figure 

 is expressed by large numerals placed above the 

 objects, while the number of times the object is mag- 

 nified is indicated by small numerals placed beneath. 

 The latter must be understood to express the number 

 of times the drawing is larger than the object in one 

 dimension. Thus, considering fig. 13, Plate I. to be 

 an inch in width (for it is really somewhat less) , being 

 magnified 150 times in the direction of the width, the 

 object itself is about T joth f an ^ ncn ^ n s ^ ze > an ^ ^ 

 is represented magnified 150 times linear, or 150 dia- 

 meters, as it is called. 



A knowledge of the number of times the object is 

 magnified is of the greatest importance in making 



c 3 



