12 MICROSCOPY FOR BEGINNERS. 



one-inch, often also called " B " or " C," will be added. 

 Opticians also make , f , J, and even ^ inch eye-pieces, 

 most of which are for special kinds of microscopical 

 work, their magnifying power being enormous and the 

 result almost worthless ; indeed, these very high power 

 eye-pieces are usually to be avoided. On no account 

 should they be selected by the beginner in microscopy. 

 Every purchaser of a stand should insist upon having 

 the two-inch, if he can have but one, as it is always use- 

 ful, and is all he will need for a long time, or until he 

 desires to use an eye- piece micrometer for the meas- 

 urement of microscopic objects, when he can add the 

 one-inch, or " B," ocular to his stand. 



The lower opening in the body always carries a screw 

 to receive the one on the upper end of the objective. 

 Several years ago the size of these screws varied widely 

 in stands and objectives of different makers, so that if 

 the student desired an objective of different make from 

 those accompanying his instrument, he was forced to 

 buy a little piece of apparatus called an adapter, one end 

 of which was made to screw into the microscope body, 

 the other to receive the objective. At the suggestion, 

 however, of the Royal Microscopical Society of London, 

 all objectives and stands now have screws of the size 

 recommended by that society, and therefore called the 

 " society-screw." Only the very cheapest stands of the 

 present day, or those having the least value as instru- 

 ments for serious investigation, are without this screw, 

 and they are usually supplied with what are termed 



