PHOTO-MICROGRAPHY. 79 



directions for developing are also his, with some alterations : — 

 (A.) Pyrogallic Acid ... ... ... i oz. 



Glycerine ... ... ... i oz. 



Methylated Spirit ... ... 6 oz. 



Mix the Glycerine and Spirit, and pour into the Pyrogallic 

 bottle. 



(B.) Bromide Potass. ... ... 200 grains. 



Liquor Amm. ... ... i oz. 



Glycerine ... ... i oz. 



Water ... ... ... 6 oz. Mix. 



(C.) I oz. of A to 15 oz. of water. 



(D.) I oz. of B to 15 oz. of water. 

 Into a measure pour, for a quarter-plate, i oz. of C solution and 

 I oz. of D; when the plate, which is now in water in an ebonite 

 dish with a cardboard cover, has soaked for a minute, pour the 

 water quickly off, and pour on the developer. If the exposure 

 has been correctly timed, the image will begin to appear in about 

 20 seconds, and in about 3 minutes will have attained sufficient 

 strength : the negative may then be slightly rinsed in water, and 

 put at once into the Alum-bath (Alum i oz., Water 20 oz.), where 

 it should stay for ten minutes, but not longer. Then wash very 

 thoroughly and immerse in a Hypo, bath (Hyposulphite of Soda 

 I oz.. Water 5 oz.) ; this should not be used too often or it 

 becomes discoloured, and stains the clear parts of the negative. 

 Wash well again after fixing. It is necessary to soak the negative 

 in water for two hours to get rid of all traces of Hyposulphite ; 

 then allow the plates to dry spontaneously, and varnish in the 

 usual manner. 



The directions given with each parcel of dry plates regarding 

 the precautions necessary to prevent injury to the plates by light, 

 should be strictly attended to. 



If the amateur is using a power that is not corrected for 

 photography, he must determine the actinic focus in the following 

 manner : — Focus the object as distinctly as possible, and expose 

 a plate ; the negative thus taken will probably be very indistinct. 

 Turn the milled head of the fine adjustment so as to bring the 

 objective away from the sHde, until the picture on the screen 

 coincides with the negative : this will be found to be the right 

 actinic focus. I am told that a piece of ground glass, placed 

 between the condenser and the microscope, gives an even, 

 opaque background to the picture, though, of course, there is 

 great loss of light ; but I have not tried this, and am, therefore, 

 not certain how far it will answer. The amateur should work 

 only with low powers until he has had considerable practice ; for 



