Photographing Ultra-Violet Spectra. 105 



The method of development preferred before all others, is that 

 originally described by Mr. B. J. Edwards. 



The materials consist of two stock solutions, the compositions 

 of which are as follows : — 



jVo. 1. — The Develojjer. 



PyrogalHc acid, . . . • -I ounce. 



Glycerine, . . . • • 1 75 



Methylated spirit, . . • • 6 „ 



]Vo. 2. — The Accelerator. 



Potassium Bromide, . . .60 gi-ams. 



A-mmonia sp. gr. -880, . • -1 ounce. 



Glycerine, . . ~^ • • • 1 » 



"Water, . . • • • 6 „ 



The solutions before use are each diluted with fifteen volumes 

 of water. 



To develope a plate, mix equal volumes of No. 1 and No. 2, 

 pour the mixture into a dish, immerse the plate, and rock the 

 dish gently. According to the nature of the sensitive films, less 

 or more of solution No. 2 may be taken. The development 

 should proceed without any forcing or local development, and be 

 completed in two minutes. The spectral lines should remain 

 dense and black after fixing. 



Mr. Carey Lea's developing solution is made by boiling an 

 excess of ferrous oxalate with 100 grains of neutral potassic 

 oxalate and 1 ounce of water. Or the following proportions may 

 be used : — 



Ferrous oxalate, . . . . -1 part. 



Potassic oxalate, . . . • 4 ,, 



Water, . . . • . IG „ 



To each ounce of the above solution is added 1 drachm of a 

 solution of 40 grains of potassic oxalate per ounce of water. 



From photographs recently taken it appears that the pyrogallic 

 developer acts more equally upon all portions of the spectrum 

 while the ferrous oxalate solution developes the image rather 

 more strongly at the less refrangible end. At first I was much 

 astonished to find that this could be the case, but a little con- 

 sideration of the different behaviour of these two developers 

 affords an explanation of how it is possible. 



