Haies — On 3IicropJiotographic Methods. 59 



yi. — Notes on MickophotoctKAphic Methods. By Eichakd A. 

 Hayes, M.D. 



[Read, April 23, 1883.] 



I HAVE the honour to lay before you some results obtained by me in 

 Microphotographic methods, in great part accomplished by the aid of 

 the grant accorded me by your Academy. 



The object which I have had in view in my experiments was to 

 obtain some simple and easily worked methods giving fairly uniform 

 results. It will be easily understood that the chief difficulty which pre- 

 sents itself in Microphotography is to obtain a source of artificial light 

 which shall at the same time have light-illuminating power, be per- 

 fectly steady, possess very active actinic properties, and be easily pro- 

 duced and maintained. 



After considerable experience with electric (arc), magnesium, lime, 

 gas and oil-lamp lights, I find that only the lime-light and the oil- 

 lamp fulfil the necessary conditions, the use of the latter being con- 

 fined to cases where the magnifying power does not exceed 50-100 

 cliams. ; or in other words, to the 1-inch or ^-inch objective. The diffi- 

 culty as to the intensity of the light is not so much in reference to the 

 exposure of the plate, as to the impossibility of getting the image 

 focussed in a satisfactory manner, the great rapidity of the dry gela- 

 tine plates now in use making the time of exposure quite a secondary 

 matter. 



The arrangement by which the photographs exhibited were made 

 is as follows : — In front of the condenser of the lime-light lantern 

 is fixed a tube, 10 inches in length, at the further end of which is 

 placed a plano-convex lens of about 2 inches focal length, mounted 

 in a sliding tube movable by rack and pinion, the beam of light 

 passing through which comes to a focus, and then whil'e only 

 slightly divergent falls on the achromatic condenser fixed in the 

 sub-stage of the microscope. This arrangement gets rid of most 

 of the heat rays, the beam passing through the condenser traverses 

 the object to be photographed, the image of which is projected 

 directly on the screen by the object-glass, no eye-piece being used. 

 I have latterly invariably used for focussing a sheet of glazed white 

 paper pasted on a glass plate placed in the dark slide, and as this 

 is simply replaced by the sensitive plate, absolute coincidence of 

 the focussing and sensitive surfaces is ensured. By focussing in this 

 manner, as one sits in front of the screen, the various adjustments of 

 the microscope and condensers are easily made, while keeping a dis- 

 tinct view of the image. 



As regards the details of focussing the image, I have latterly 

 adopted the following method : — 



The object having been brought into the desired position and 



11. I. A. PltOC, sun. II., VOL. IV. SCIENCE. K 



