Photo-micrography is that special branch of photography which has for its aim the production of pictures of magnified microscopic objects. Its application dates back many years, even in the days of the old Daguerreotype process.

Improvements in photography, especially the introduction of gelatine dry plates, have so much shortened and simplified the methods pursued, that to any microscopist possessing a slight knowledge of photography, the work becomes comparatively easy after a little practice.

The apparatus required is simple, consisting of a microscope with a good fine adjustment, a camera, and a base-board on which to arrange these and the source of light. For work with lower and medium powers, a good paraffin lamp is found most convenient, It may be either a duplex or a single-wick lamp. An ordinary passage lamp with a plated reflector answers capitally.

Numerous experiments with electric light have not proved its sufficient superiority for this work to compensate for the additional trouble and expense involved. The centre of the lamp flame and the axis of the condenser, object glass, and eye-piece must be in the same line, and should be at right angles with the focussing [sic] glass of the camera.

Some operators dispense with the eye-piece, and use an extending camera, but this was not recommended by the authors. It is well known that objectives, especially those of large angle, give a sharp image of but a small portion of an object possessing any appreciable thickness. By careful focussing, images of successive portions or planes may be obtained, and the combination of these in the mind gives it an idea of the structure of the whole, but this, of course, cannot be done in a photograph; only those parts actually in focus are depicted.

The powers employed in the production of the pictures to illustrate the paper were 4in., 2in., 1in., 1-5th in., and 1-10th in., with exposures varying from 20 seconds to 5 minutes for transparent objects, and 10 minutes for opaque objects. Microscopic objects not being specially constructed for photographic work, do not, as a rule, give the best results at their ordinary visual focus; in other words, their chemical and visual foci are not usually co-incident.

This applies more particularly to the lower powers, and these require a varying amount of correction. This is made by slightly withdrawing the objective from the object. After the requisite exposure the plate is treated exactly as if it were a portrait or landscape.

A very convenient for working is the quarter plate (3 1/4 by 4 1/4), as the circle obtained on this is exactly suited for the production of transparencies for the lantern. From the negative thus obtained, a positive has to be taken, and this when mounted is a lantern transparency. Of all methods yet made use of for the illustrations of lectures on the microscope, that by means of lantern slides is the most beautiful and effective.

The lantern microscope, which magnifies the object itself, is limited in its application and unsatisfactory in its results. Even with the best appliances it is difficult to obtain a well-illuminated disc above 3 feet in diameter – a size not at all suited for a large audience, and scarcely for a small one. On the other hand, with photo-micrographs prepared as lantern slides, illustrations magnified to any extent can be shown, the only limit being the size of the screen and the intensity of the light.

A large number of pictures were exhibited on the screen bt means of the oxy-hydrogen light, each picture being carefully described. Among the most successful may be mentioned:- The section of the eye of a cockchafer, the cones and tubes being beautifully clear; the tongue of the drone fly; the spiracle or external opening in the breathing apparatus of a fly; the tongue of a cricket and of the honey bee; also a few specimens of diatoms, especially heliopelta, arachnoidiscus (taken with the tenth objective and showing great depth of detail, and the beautiful aulacodiscus. Two specimens of triceratium, including the variety septangulayum were very distinct.

The “bathybius” of Huxley, including cocoliths and coccospheres was well shown, as also were the opaque pictures of Foraminifera and Polycystina.”