The President called upon the Secretary (Mr. Stiles) to give his paper on “Improvements on Photomicrography”.

The lecturer stated that during the past few years very considerable improvements had taken place in that department of Photography which had for its object the delineation of microscopic objects. These were of three-fold characters, embracing the arrangement of apparatus including methods of illumination, improvements in objectives & improvements in Plates.

After a thorough trial of the two systems of working with the eyepiece & without, Mr. Stiles had come to the conclusion that better results were obtainable by the latter method: the field being flatter & the general definition consequently more perfect. The plan of working without the eyepiece necessitated the use of a longer camera & of a special appliance for turning the milled head of the fine adjustment.

It is a great advantage to have the microscope & lamp arranged on a separate baseboard especially when the higher powers are employed, the object can thus be singled out & all adjustments made with the minimum of trouble & under direct observation. When everything is satisfactory arranged the eyepiece is withdrawn, a black-lined tube put in its place & the microscope baseboard with the illuminating apparatus attached placed on the general baseboard which carries the camera.

In setting up the apparatus everything is adjusted so that the centre of the flame, the axis of the condenser & of the microscope & the centre of the plate are in the same line. With the higher powers this is especially important. As a source of light, a single wick paraffin lamp was found to answer capitally for all powers up to & including a 1/12 numeration. The lamp was used with the edge of the flame turned to the stage, the rays being parallel by a Bulls Eye condenser placed with its flat side close to the flame & at a distance of about 8 or 9 inches from the stage. For powers of ½ inch & upwards an Achromatic Condenser was employed at its focal distance from the object: for low powers, 1 inch to 4 inch, a double convex lens of 2 ½ inch focus was substituted for the achromatic condenser & gave excellent results also with the 4 inch the flame of the lamp placed slightly obliquely.

In working with ordinary plates, objectives as formerly made usually required a certain amount of correction for the want of coincidence of their visual & chemical rays. Objectives can now be obtained specially corrected for photomicrography. A simple & easy plan of ascertaining the amount of correction required with any objective was shown & specimen trial plates were exhibited. The importance of accurate focussing was insisted on & the lecturer explained his method of doing this & exhibited the apparatus employed. The latter which was very simple & effective consisted of a wooden block replacing the ordinary focussing screen pieced by a hole about 2 ½ inches in diameter, a brass plate sliding over the hole carried an aperture for the No. 1 eyepiece, the position of the latter being so adjusted that when a object was in sharp focus on the ground glass it was also seen at its best through the eyepiece.

The advantage of this method is especially apparent with high powers.

The value of Isochromatic Plates in photomicrography were so obvious that they no sooner became an article of trade than they began to be employed for this work. It is well known that the dark brown chitinous tissue of insects is particularly non actinic & that deep coloured insect preparations show very little detail in their shadows.

This defect may to a very great extent be overcome by the use of Isochromatic plates.

But there are other important advantages which the lecturer believed had up to the present time been pointed out.

These plates are extremely sensitive to artificial light so much so that Edward’s medium Rapidity are 8 to 10 times as rapid as an Ilford ordinary plate.

Further experiments on another point are required before a definite opinion can be given, but the lecturer had every reason to believe that with these plates no correction for want of coincidence between the usual & chemical rays were required with objectives that needed it in working with ordinary plates.