INTRODUCTORY. 



form of a reading-glass or hand-magnifier; perhaps 

 the most useful form for the pocket consists of one 

 or more lenses, which shut up in a tortoiseshell or 

 horny frame, with an intervening perforated plate 

 to act as a diaphragm when the lenses are used alto- 

 gether. The micrpscopist should never be without 

 this little pocket-magnifier ; it will be very useful in 

 examining samples of water containing animalculae, 

 revealing to him the 

 presence or absence of 

 some particular kinds 

 he maybe in search of, 

 or enabling him to gain 

 some clearer idea of the 

 structure of a fern, grass, 

 or flower, than the un- 

 aided eye can afford. 

 Simple microscopes, 

 properly so called, are 

 supported on stands. 

 That one known as the 

 Society of Arts Simple 

 Microscope, manufac- 

 tured by Mr. Field, 

 of Birmingham, is a 

 useful form of simple microscope. It has a tubular* 

 pillar about five inches high, which screws into the 

 lid of the box which contains the instrument when 

 not in use ; a concave mirror is fixed at the lower 

 end of the pillar, while the upper end carries the stage 

 and a short horizontal arm in which the lenses, three 

 in number, may be screwed. A condensing lens, for 

 opaque objects, can be fitted into any of the four holes 

 with which the stage is perforated. This instrument 

 has a range of powers from 5 to 40 diameters. 



What is the difference between a simple and a 



A Simple Microscope. 



