72 J. Waterliouse — Photography in connection with [No. 2, 



This was effected by the use of a tappet or make-circuit key, to which 

 Colonel Tennant had very ingeniously fitted a pair of scissors so that the 

 act of cutting the thread to let loose the exposing shutter of the photohe- 

 liograph, completed the circuit and the exact time of exposure was thus 

 instantaneously recorded on the chronograph. The Janssen slide was also 

 fitted with arrangements for being placed in electric communication with 

 the chronograph, so that every turn of the winch was recorded at the 

 moment of exposing each picture round the circumference of the plate. 



The staff* of assistants at my disposal included three European assis- 

 tant-photographers, Sergeant J. Harrold, E. E., of the Photographic 

 Branch Surveyor General's Office, Calcutta, Lance-Corporal George and 

 Private Fox, of H. M.'s 55th Eegiment, who had been thoroughly trained 

 by Colonel Tennant in the ordinary manipulations of the wet collodion 

 process, with three native servants for handing the plates to and fro and 

 performing other menial duties. 



Preparatory Work and Drills. — One of the first things to be done 

 before beginning the drills was to examine the whole stock of glass and 

 carefully select about 200 of the best and most free from flaws, which were 

 carefully set aside to be used for the Transit. 



The dry plate trials were resumed with the advantage of having a 

 suitable instrument to work with. The beer-albumen and other processes 

 that had been found more promising in Calcutta were tried again, but 

 were found not quite satisfactory with the sun ; the tea and coffee 

 processes, which I had not tried in Calcutta, were better and I finally 

 adopted a modification of the coffee process recommended by M. Con- 

 stant of Lausaune, substituting albumen for gum to avoid the tendency 

 to blistering so common when using gum, and also with the view 

 of lessening photographic irradiation, against which the coffee proved a 

 further protection. These plates were easily prepared and were found fairly 

 sensitive, easily intensified, perfectly clear and free from blurring in the 

 shadows. 



The glass plates, having received a thin coating of albumen as a subs- 

 stratum, were coated with collodion and sensitised by a somewhat prolonged 

 immersion in a 40-grain silver bath, then washed in four changes of dis- 

 tilled water and finally immersed in a resensitising solution, or so-called 

 preservative, composed of 



Dried albumen 2 grammes 



Sugar 12 „ 



Coffee infusion made by boiling 30 grammes of 



coffee in 360 C. C. of water 300 cub. cents. 



Water 300 „ „ 



and then drained and dried without heat. 



