194 THE entomologist's record. 



of a want of practical experience in plain photography. I do not, 

 however, minimise the importance of a knowledge of the optical 

 principles involved in the use of the microscope. The usual method 

 of photographing with the microscope is by the employment of an 

 ordinary photographic camera, one having a triple extension for 

 preference. The microscope is brought to the horizontal position, 

 and the upper end of the tube attached to the camera front, at the lens 

 aperture, by two loose inter-fitting flanges, so as to exclude the light. 

 The camera lens is, of course, dispensed with. The object is 

 then illuminated by the direct rays of a lamp exactly in the 

 optical axis of the microscope, a bull's eye condenser being placed 

 between it and the substage condenser. For low and medium power 

 work the microscopic eyepiece is quite unnecessary. Indeed, the 

 camera itself may be dispensed with, the principle being that the micro- 

 scope and illuminant are screened of!" from the sensitive plate by means 

 of a box having one side removed and replaced by a dark curtain. The 

 room being dark, takes the place of the camera chamber. The image 

 is focussed on the screen in a plate-holder, which can be adjusted on 

 a sliding base to the required distance from the microscope, this 

 distance depending on the amount of magnification required. The 

 advantages of working in this way are — that a dark slide is unnecessary, 

 and thus any movement after final focussing is obviated ; the danger 

 from reflected light is also less. Accurate focussing is not possible on 

 the ground glass screen, on account of the coarseness of its grain, so 

 after roughly focussing the image on the latter, we replace it by a piece 

 of plain glass and focus the serial image with an ordinary photographic 

 focussing lens. When the degree of magnification required necessitates 

 a long camera extension, we have to focus by means of a rod fixed on 

 the base-board, and attached at its further end by a leather band to the 

 fine adjustment of the microscope. No definite guide here can be 

 given as to the length of exposure, as it depends on the following 

 factors — the objective used, amount of magnification, aperture of 

 diaphragm of substage condenser, character of illuminant, speed of 

 plate, and colour or density of object. A few trial exposures will, how- 

 ever, soon determine this. Hitherto, I have been treating of the 

 photography of transparent objects, but, when dealing with opaque 

 objects, such as eggs, etc., we have to use reflected light. The 

 simplest method of illumination is by means of the bull's eye condenser 

 interposed between the source of light and the surface of the object. 

 The length of exposure is considerably more. As a general rule, when 

 photographing insect preparations, a coloured screen is not required. 

 When these are of a dark chitinous character, the difficulty can usually 

 be surmounted by giving increased exposure with dilute prolonged 

 development. Pyro-soda, with plenty of sulphite, is the developer I 

 recommend. Isochromatic plates are necessary, and they should be 

 " backed." 



For purposes of reproduction for book illustration, and for 

 obtaining the maximum amount of detail in the resulting print, I 

 cannot insist too strongly on the use of a glossy paper of the print-oat 

 type. Contrast is improved thereby, and it is my experience that the 

 process worker prefers this class of print to the matt bromide and 

 others of this character. 



Space will not permit to speak at any length on the prepara- 

 tion of lantern slides, it will be sufficient to remark that ^ plate 



