314 



RICHARD M. HOLMAN 



purpose. A photographic lens of rather short focal length had 

 been employed in this drawing camera and the image had been 

 traced on a piece of almost transparent parchment paper held 

 against the glass plate by means of two pieces of wood wedged 

 into the ground glass frame. 



I found it very difficult to trace accurately the image because 

 the drawing surface was perpendicular. On that account I de- 

 signed the attachment which is illustrated in the accompanying 

 figures to bring the image into a horizontal plane. It was con- 

 structed by a photographic mechanician in Leipzig and was so 

 made that it could be substituted for the ground glass frame of 



r \v 



Fig. 1 . Section through the drawing camera. One-sixth natural size. Expla- 

 nation in the text. 



the camera by sliding it into the grooves which held the frame 

 in place. The attachment consisted of a wooden box having 

 approximately the form of a right triangular prism, two sides of 

 which were open. One of these open sides was held against the 

 back of the photographic camera. Into the other open side, 

 which was horizontal when the box was in position, a glass plate 

 (g) was fitted. On the inner surface of the hypotenuse side of 

 the box a mirror (m) was fastened which reflected the pencil of 

 light coming from the camera lens upward through the glass 

 plate. 



A very satisfactory contrivance which I had constructed for 

 stretching the parchment paper over the surface of the glass and 



