April, "09] JOURNAL OF ECONOMIC ENTOMOLOGY 97 



lenses are quickly attachable to a set of interchangeable lens-boards 

 which fit this camera. 



"We have a complete series of Zeiss microscope objectives as well 

 as various others, and find it a great convenience to have a long se- 

 ries, as we can always secure the degree of magnification and at the 

 same time size of image that we require. 



Magnification. — In our work on scale insects we have found it de- 

 desirable to secure the required size of image by the use of a high 

 power lens and short bellows rather than with a low power and longer 

 bellows. This we have done for the sake of securing greater detail in 

 the print. At the same time it is desirable to bring the whole ob- 

 ject into focus if possible, and the higher the power used the less is 

 the focal depth. One may, with a lower power and longer bellows, 

 produce as large an image, but no more detail can be expected than 

 is brought out by the power of lens being used. 



In photographing thicker objects Avhich present much detail, it 

 is necesary to use a lower power and, if the length of bellows is not 

 sufficient to produce the size of image desired, it is necessary to make 

 enlarged copies from the negatives or prints. 



' Plates. — "We have used several kinds of plates but prefer one made 

 to our order by the M. A. Seed Company. This plate is their regular 

 lantern slide emulsion on 4 by 5 glasses. It is difficult to estimate 

 closely the proper exposure for scale insects of varying density and 

 this plate allows us greater latitude in that respect and results in a 

 saving of both time and plates. 



Prints. — We have thought it desirable to dissolve out the back- 

 ground of our prints and obliterate parts of the image not required. 

 This is done as the prints are removed from the fixing bath, by the 

 use of a solution of hypo and potassium-fenn-cyanide. The print is 

 placed, face up, on a piece of glass over a tray containing the solution. 

 A swab of absorbent cotton is dipped in the solution and applied to 

 the parts to be dissolved out. The glass is inclined so as to allow the 

 solution to run away from the print and into the tray. 



Regular glossy Velox paper is used when it is desired to obliterate 

 parts of the print but, in general, Solio papers are to be preferred. 

 The Velox prints are dried on a ferrotype plate as with Solio papers. 



Chairman Brittox : There is now a chance for a discussion of 

 this paper. 



Mr, Skinner : I wish to say that we have trouble in using the ordi- 

 nary lantern slide plates. I would like to ask Professor Cooley 



