April, '09] JOURNAL OF ECONOMIC ENTOMOLOGY 93 



be made in any quantity, using' the following proportions, by thor- 

 oughly dissolving in water in the order given. 



1 oz. Metol. 



2 oz. Hydrochiuou. 



16 oz. Sulphite of Soda. 

 14 oz. Carbbnate of Soda. 

 60 grains Potassium Bromide. 

 320 oz. Water (distilled or boiled). 



Directions for use.- — For Yelox and kindred papers, full strength; 

 for ordinary plates, stock solution 1 part, water 1 part ; for films and 

 •double coated plates, stock solution 1 part, Avater 2 parts. 



Operations. — One of the most important operations of photography 

 is the proper focusing of the image on the ground glass. At high 

 magnification the image is so obscure that it is often necessary to 

 use a focusing glass. A focusing glass may be purchased, or it is 

 •comparatively simple to make one from an ordinary dissecting lens 

 mounted in a cylinder of proper length, according to the focal dis- 

 tance of the lens. This focusing lens is placed on the ground glass 

 and enables one to secure much greater exactness than is possible 

 -with the naked eye. After the object is properly focused on the sur- 

 face nearest to the camera, by stopping down the lens it will be seen 

 that the depth of focus is increased wonderfully as the diaphragm 

 orifice is reduced, thus bringing all parts of the convex insect into 

 «harp focus. If the lens is focused on the portion of the insect 

 farthest from the camera, stopping down the lens will not bring the 

 nearer portions into sharp focus, as objects beyond the original point 

 in focus only, are brought into sharp focus by stopping down the 

 lens. It must be remembered that in judging the time of exposure 

 the stop at which the lens is placed and the bellows length all contri- 

 bute to variation in the time. As one enlarges from natural size, each 

 full diameter enlargement requires double the amount of exposure 

 required at the previous enlargement. With the stopping of the lens 

 the time of exposure is almost squared. 



It is often desirable to make two or three, or even four, exposures 

 ■of an insect from different points of view on the same plate, such as 

 dorsal, lateral, ventral views, etc. This seems at first a rather diffi- 

 cult proposition, but by the use of two diaphragms, each covering 

 one-half of the photographic plate, dividing the surface in half length- 

 wise and crosswise, any four separate exposures may be made on the 

 •same plate by simply shifting these half diaphragms. These dia- 

 phragms may be made of black cardboard, or better still, of hard 

 rubber plates, such as are used in an ordinary plate holder. These 



