354 



MAGNIFICATION OF DRAWINGS 



[Cn. X 



Briefly stated, if one has an object of known size, then the size of 

 the image divided by the size of the object will give the magnifica- 

 tion in every case. In the example given above the object is i mm. 

 and the image is 25 mm. : 25 -=- i = 25. Or, if one took a single 

 space as object, that is, half a millimeter, then the image would 

 measure 12.5 mm., and 12.5 -=- .5 = 25 as before (see sioa). 



FIG. 198. SPENCER LENS COMPANY'S APPARATUS FOR DRAWIM; WITH 



THE MICROSCOPE. 

 (Cut loaned by the Spencer Lens Co.). 



This consists of a small arc lamp with the proper wiring, rheostat and con- 

 nections for the house electric supply. The lamp has all the adjustments, and 

 the condenser tube is telescoping so that the beam of light may be parallel or 

 converging. 



The microscope is supported on an adjustable shelf which can be raised or 

 lowered on the vertical rods, thus enabling one to get any desired magnification. 



The vertical supports for the microscope shelf serve to carry a curved metal 

 band to support the cloth curtains to shade the drawing surface. There are 

 two curtains and they hang freely, thus avoiding all interference with the 

 hands in drawing. If one desires, the arc lamp can be put in line with the 

 microscope and the mirror turned aside. 



For a reflector beyond the ocular a prism is used, thus avoiding any of the 

 defects of a mirror. 



