148 



PEACTICAi TBEATISE ON THE MICROSCOPE. 



server may use either 

 his right or his left 

 eye. The back of the 

 recesses for the nose 

 must be made of 

 black silk or stuiF, 

 but not closed at the 

 bottom to confine the 

 breath, which would 

 make the eye-glass 

 dim. 



Goniometer. — A 

 very valuable instru- 

 ment for measuring the angles of minute crystals, known as 

 the goniometer, the invention of Dr. Leeson, is capable of 

 being applied to the microscope, and is furnished by Messrs. 

 Smith and Beck for this purpose. As some little time is 

 required before an observer can get into the way of using it 

 with faciUty, it has been deemed best to give a detailed 

 description of it in a separate chapter. 



The various modes of employing the knives, forceps, dis- 

 secting and all other instruments supplied with the best micro- 

 scopes, will be considered in full in other parts of the work. 



Fig. 104. 



