CH. X] DRAWING WITH HOUSE CURRENT 345 



495. Microscope. Any modern microscope with a good sub- 

 stage condenser can be used, provided it is supplied with a flexible 

 pillar, so that the tube can be made horizontal; and provided also, 

 that the fine adjusting mechanism will work when the tube is 

 horizontal. 



There must be a prism or mirror beyond the ocular to reflect the 

 image-forming rays downward upon the drawing surface (fig. 192). 



The discussion of avoidance of distortion, the proper objectives, 

 oculars, etc., to use, which was given in the earlier part of this 

 chapter apply here ( 452, 483). 



496. Position of the microscope for drawing. In the drawing 

 outfits thus far devised, the microscope is placed in one of the 

 following positions : 



(1) In an inverted position with the objective pointing directly 

 upward (as in the large Edinger apparatus, fig. 202). 



(2) Inclined at 45 degrees (as in the small Edinger apparatus, 

 fig. 204). 



(3) In a horizontal position (fig. 192). 



With the microscope in an inverted, vertical position, there 

 should be no distortion of the image if the drawing surface is 

 horizontal. 



With the inclined microscope, the mirror used must be so inclined 

 that it throws the image directly down upon the horizontal drawing 

 surface, or the image will be distorted. It is not easy to tell just 

 the inclination of the microscope, and therefore, the exact inclina- 

 tion to give the mirror, to make the axial ray perpendicular to the 

 drawing surface. In the small Edinger apparatus (fig. 204), the 

 directions are to make the inclination of the microscope 45 degrees 

 and the inclination of the mirror 22^ degrees. This arrangement 

 will give a correct image. One may need to use a protractor to 

 make sure that the inclination of the microscope and mirror are 

 exactly correct. 



With the horizontal microscope, the mirror or prism is so 

 arranged that it is fixed at 45 degrees and therefore if put directly 

 over the ocular of the horizontal microscope, will reflect the light 

 perpendicularly upon the drawing surface, thus avoiding distortion 

 (see 483). 



