186 Capt. J. Waterhouse on [Jan. 20, 



of sulphate of potash and sand -^ inch thick had formed across the mid- 

 dle of the bend. Strong sulphuric acid and potash were again poured 

 into the limbs, and were now only separated by a thin plug of sulphate 

 of potash. Platinum electrodes dipped into the liquids. Electromotive 

 force 139. The circuit was closed for ten minutes. 



E. F. 



14 seconds after insulation, 31 



20 



>> 



39 



40 



»» 



44 



1 minute 



»> 



48 



3 minutes 



>» 



74 



5 



>> 



89 



10 



>* 



98 



20 



»> 



105 



65 



>» 



119 



The wires were again connected and the circuit left closed for about 

 twenty-four hours. It was found that the plug had extended for about 

 half an inch on the side of the sulphuric acid by the formation of crystals 

 of sulphate of potash, but had not apparently changed where it was in 

 contact with the potash. 



X. A similar plug was formed in a second tube. Into one limb sulphuric 

 acid, with a small quantity of permanganate of potash, was poured, into the 

 other caustic potash : E. P. = 178. Circuit was closed for ten minutes. 



E.F. 

 10 seconds after insulation, 90 

 20 „ „ 110 



40 

 1 minute 

 3 minutes 



9 

 19 



123 



128 

 138 

 148 

 150 



II. "On Reversed Photographs of the Solar Spectrum beyond the 

 Red, obtained on a Collodion Plate/' in a Letter to Prof. 

 Stokes. By Captain J. Waterhouse, Assistant Surveyor- 

 General of India. Communicated by Professor Stokes. 

 Received November 29, 1875. 



Surveyor-General's Office, 



Calcutta, November 5, 1875. 



My deae Sie, — I have the pleasure to send you, by Overland Parcel 



Post, for presentation to the Royal Society, two photographs on glass of 



the solar spectrum, showing the extreme red rays below A, obtained on 



a dry collodion plate prepared with bromide of silver stained with a blue 



