S52 



PIKE'S, JR., DESCRIPTIVE CATALCGL T E. 



ions have a clear and open appearance. The design, J, J, 

 is permanent on the board, showing its method of nse. 

 A sheet of drawing-paper is inserted by pressure at ', '??, 

 alternate, in a few moments. The board is a combination 

 of several valuable instruments, 

 united to qualities decidedly its 

 own ; therefore the operator in 

 its use will set aside the use of 

 single instruments, and act at 

 once on general principles. The 

 best materials are thoroughly 

 combined in its construction, 

 and the board makes a handsome 

 appearance. 



Price of draughting-board and 

 T rule, $10. 



The Compound Microscope is 

 employed where the investiga- 

 tion of minute objects are re- 

 quired, and an observer wishes 

 sufficient magnifying power to 

 reveal them in their perfect de- 

 velopment. It consists of three 

 parts, the optical part containing 

 the object-glass and eye-piece, 

 the stage for holding the object 

 to be viewed, and a mirror or con- 

 densing lens for illuminating the 

 object. However various the 

 mechanical arrangement, these 

 parts are found in all, and the 

 principle of their management 

 the same. 



The Compound Microscope 

 (Fig. 787) consists of a stout 

 brass tube mounted on a brass 

 foot or base ; a portion of the 

 tube is cut away for the stage 

 on which the object to be view- 

 ed is placed; below there is a 

 circular opening in the tube for 

 the light to fall on the mirror, 



