354 W. IMBODEN ON A SIMPLE DRAWING AND PROJECTION APPARATUS 



A piece of ordinary good-quality mirror, about 4x3 inches in 

 size, is fixed to a metal arm about 4| inches in length. This arm 

 is connected with the draw-tube of the microscope by means of 

 a clamping ring. A glance at Fig. 1 will make the arrangement 

 clear. The mirror is fixed to the supporting arm in such a 

 position as to face the front of the ocular at an angle of 45°. It 

 can, of course, be brought nearer to or farther from the ocular 

 by sliding the arm in or out, thus providing a ready method of 

 securing a certain range of magnifications without changing the 

 objective or the ocular. 



Fie. 1. 



A drawing surface lying horizontally upon the table receives 

 the projected image. 



It is next necessary to protect the image from any extraneous 

 light which would tend to impair its brilliancy, and with that 

 end in view we have to consider some kind of light-excluding 

 appliance. A camera obscura would certainly be the most effec- 

 tive arrangement if the brilliancy of the projected image were 

 the sole consideration ; but as we find in practice that an almost 

 even illumination of the whole drawing surface with a small 

 balance in favour of the image itself constitutes the most favour- 

 able condition to execute and follow the progress of the sketch 

 in hand, we do not require more than a small screen to control 



