14 On the Photographic delineation [No. 9, kiw series. 



The other end of the cylinder should be furnished with a drawing 

 string. A new front might be made for this purpose, but it is 

 not necessary, for, if the cylinder of velvet be a little loose, it will 

 not be found at all in the way when the Camera is required for 

 other work. 



3rd. There is a difficulty about the focusing screen, and I have 

 not yet found a good material for this purpose. The common 

 ground glass screen forms an infinity of prisms which, when the 

 object is strongly illuminated, as by the sun, render a sharp well 

 defined outline impossible. The iodized and washed collodion 

 plate, recommended by Mr. Shudbolt, is somewhat better, but a 

 focusing screen for the Microscopic Camera is still a desideratum. 



The foregoing is all the additional apparatus required. When 

 wanted for use place the platform upon a tolerably firm table in 

 some convenient spot in the open air, as near as possible to the 

 operating room, and if the place selected be such that either sun- 

 shine or shade may be had at pleasure, by moving the table a foot 

 or two, so much the better. Little more than the mirror should 

 be exposed to the sun, and this only while focusing, or exposing 

 the plate. At other times the table should be removed into the 

 shade, or the exposed portion of the apparatus should be sheltered 

 by an umbrella held by an assistant, for the intense heat of the 

 sun for any length of time would, in all probability, injure the 

 cementing of the object glasses. 



The best general position for the table is parallel with the 

 sun's rays, with the Camera nearest to that luminary. It will be 

 found convenient to place the edge of the board close to the right 

 side of the table, and the end of the Camera flush with the end 

 of the table. 



The platform having been thus fixed, put the Camera into its 

 place, and then the Microscope. Having turned the body until it 

 is horizontal, push the foot-board along until the eye-piece is just 

 inside the Camera. Tie the velvet cylinder tightly round the 

 body of the Microscope, and place the focusing screen at ten 

 inches from the focus of the eye-piece. 



The usual diameter of the field at ten inches from the lowest 

 eye-piece is five inches, and a square of this size should be mark- 



