1898.] 105 



Now for the background (2). "When taking insects by artificial 

 light the background is simply a piece of white cardboard, but for doing 

 transparent wings a special arrangement has to be brought into play, as 

 I will explain presently. (3) are incandescent gas lamps, which may be 

 changed to oil lamps if more convenient, though the exposure will be 

 much longer, the light from oil being slightly yellow, consequently 

 less actinic. (5) is the end of a brass tube to be joined to ordinary 

 india rubber gas tubing, which is connected with the nearest gas 

 bracket. The two tubes from the lamps are connected by a brass Y? 

 so that one bracket does for both lights. (4) is an archimedean screw 

 for fine focussing, but the front part of the camera (7), and the base 

 board (8) of background, &c., both move backwards and forwards by 

 hand for rough focussing and to get the desired amount of enlarge- 

 ment. (6) is the focussing sci-een. The lamps have reflectors that 

 are not shown in the diagram, as they would hide some of the details. 

 The way to use the instrument in daylight is somewhat different. 

 It is put facing a window, i. e., the source of light is behind the back- 

 ground. The sheet of white cardboard (2) is left in the frame (9). 

 (The frame is of course grooved to enable the backgrounds to slip in 

 and out). The lamps are removed, and in their places are put two 

 small mirrors (about 8 inches in diameter) on stands facing the window. 

 They reflect the light on to the specimen, and the backboard being 

 white makes the insect stand out nicely. It is well to have the mirrors 

 fastened to their respective stands by a ball-and-socket joint, so as to 

 enable them to be arranged at any angle, something like a stand bull's 

 eye condenser for a microscope. The greater the enlargement the 

 more difficult it is to get a nice even lighting, as the specimen has to 

 be so close to the objective. This difficulty is more easily overcome 

 by artificial light. 



Of course an ordinary camera can be utilized for this kind of 

 thing if the bellows is of sufficient length, in conjunction with oil 

 lamps, by the display of a little ingenuity as explained in the April, 

 1897, number. 



For bright and multi-coloured specimens it is necessary to use a 

 yellow screen and orthochromatic plates to procure the proper value 

 of the colours in monochrome. 



Capt. Abney, E.E., F.lt.S., says in one of his works: — "The 

 object of orthochromatic photography is to render the image produced 

 on a print of the same relative luminosity that the colours in the 

 objects appear to the eye." The yellow screen is a necessity, for, to 

 again quote Capt. Abney: — "Orthochromatic plates, without the ex- 



