PHOTO-MICROGRAPHY A veryawkward word is this, and one which somehow sticks in the throat of its user in a most disagreeable manner. Why not Microphotography? Sad to say, the latter term has already been annexed by the authorities, to describe the tiny photographs of scenery or country life which we used to find in ivory pencils or paper knives bought at the seaside. The field of photo-micrography is a very wide one indeed, embracing the vast insect population of the world, not to speak of the cellular growth of the whole vegetable and animal creation, great and small, or that unknown world of protozoa and bacteria, with which we are acquainted only through the medium of the high power microscope. It stands alone as the only method of recording observations made in the regions visible through the microscope, the work of the hand craftsman being quite worthless. We may divide this field into three sections : (I) Low-power photo-micrography, which is concerned with the photography of subjects needing only a magnifica tion ranging from two to sixteen diameters ; (2) medium power work, in which the magnification rises from eighteen to about 300 diameters ; (3) high-power or critical photo micrography embracing magnifications from 500 diameters onwards, and of course demanding most accurate instruments, combined with the highest skill and experience.
Low Power .Micrographs.—Although these include by no means the least interesting class of subjects, the apparatus required is very simple, in fact any kind of enlarging lantern can be adapted. A thin wood slide, the size of the ordinary dark slide or enlarging lantern slide, may have a circular hole cut in its centre, about 4 in. in diameter, and a beading glued above and below, of the proper size to take the usual glass microscope object slides. Focussing must be done with the usual ruled glass plate. This method will serve very well for the enlargement on to a quarter plate of any fairly transparent object, such as an ant, spider, caterpillar, or other winged insect.
A daylight enlarging camera is to be preferred to the enlarging lantern, in which the condenser is so near the object. And if the operator possesses a camera of the old
fashioned type, focussing backwaids, i.e. in which the front is fixed, and the focussing screen travels towards the operator, a still more serviceable contrivance may be erected, and one which will serve for opaque objects to be photographed by reflected light, as well as those which, being transparent, are photographed by transmitted light.
Having a piece of wood of the same width as the camera and about four feet long, the camera must be clamped at one end. Remove the sliding front carrying the lens, and fit it to the front of a large oblong box of cardboard, of the same diameter as the camera front, and carefully blacked inside with Brunswick black. This card board box is open at the back, and has a cloth hood glued on it, which covers an inch or two of the bellows and is held in position by a rubber band in one of the folds. A piece of wood, glued to the front part of the cardboard box at the bottom, will make it correspond in height with the baseboard of the camera. This will form an extension to fit into the front of the camera ; extensions properly made, with bellows fitting either in front or behind the camera, are now to be obtained from camera makers for a few shillings.
The object must be raised on a stand to the same height as the lens, and behind it is introduced either a magic lantern with its front lenses removed, or some kind of condenser and lamp. A piece of ground glass between the condenser and the object (provided it is out of focus, or the ground surface will enlarge and show a grained image on the plate) will diffuse illumination and improve results considerably. Great care must be taken that lens, object, and condenser are well in one central line.
For all microscopic work backed plates should be used, preferably isochromatic, but when the illuminant is either oil or incandescent gaslight we need not always employ the yellow screen. Development should be very fully carried out, glycin or pyro-caustic soda being very suitable developers. An under-developed photo-micrographic plate is utterly useless.