THE CAMERA, ETC. 43 



been found, of sufficient surface opacity and fine- 

 ness of texture, to take the place of patent plate. 



The second may be remedied by magnifying the 

 image. A focussing glass answers this purpose, an 

 excellent one being made as follows : 



With a piece of stout cardboard make a tube four 

 or five inches long to fit one of the eye-pieces of the 

 microscope, and blacken it inside. In the opposite 

 end fix a plano-convex lens about three inches focus, 

 its convex side being turned towards the eye-piece, 

 or preferably a universal screw to receive an ob- 

 jective of about the same power. Make another 

 tube six or seven inches long to fit over the first, and 

 the focussing glass is completed. 



The end of the outer tube being placed against 

 the screen, its roughened side is brought into focus 

 by sliding the inner tube within the outer. When 

 the best focus has been obtained, which may be done 

 by fastening a very small fly or other minute object 

 on the focussing screen, the inner tube is marked 

 with a circle where it joins the outer, thus enabling 

 it to be placed in the same position when again 

 required. 



The third difficulty, namely, want of light, cannot 

 be overcome, as any increase in quantity of the light, 

 decreases the visibility of the structure. 



The stand intended to support the microscope and 

 its accessories requires to be made as firmly as possi- 

 ble. The following is a description of the form 

 finally adopted by the writer after more than ten 



