C^Q Col. Watcrliouse — Electro-chemical Eeversals [April, 



hritavarman, as inscribed on the paper, in wliich the coins were received, 

 is certainly read wrongly. For the reading varman there is absolutely 

 no ground on the coins ; Jcrita may be correct ; though the letters on 

 the coin look more like kriga. 



The fourth coin belongs to the same class of the so-called later 

 Indo-Scythian coins of the " Kida " type ; but to a different variety. 

 The obverse shows, as usual, the standing figure of the king, with keda 

 under his left arm ; under his right arm are two letters ^11 kasa or T^ 

 rasa ; on the proper left margin there is a mutilated ^^ sha. The 

 reverse shows the seated form of the goddess, and along the proper 

 left margin ^ ^^ S'ri Ghachcha with faint traces of another (probably) 

 conjunct letter. The full legend may have been §t ^^^ /SV^' Ghach- 

 chasga, i. e., " of the illustrious (king) Ghachcha." The name " Ghach- 

 cha " appears to me perfectly clear on the coin ; and I am disposed 

 to ascribe the coin to the well-known Raja Ghach of Sindh, whose 

 history is related in the Ghachnama (see Sir H. Elliot's History of India, 

 Vol. I, p. 131). He reigned about 650 A. D. 



GoLONEL Waterhouse exhibited some silver and glass plates show- 

 ing reversed deposits obtained by passing electric currents through 

 photographic ' developers ' containing thio-carbamides and said : — 



At the meeting of the Society in August last, I exhibited some 

 specimens of a curious reversal of the photographic image produced by 

 adding small quantities of thio-carbamides or sulpho-ureas to the 

 ordinary eikonogen developer, and showed that although reversal of 

 the image was by no means uncommon, it was usually caused by over- 

 exposure or some other abnormal action of light, whereas to produce 

 these new reversals even less than the ordinary exposure was sufficient, 

 and they appeared to be entirely due to some peculiar action of the 

 thio-carbamide added in very minute quantities to an alkaline eikonogen 

 developer. 



At that time I was quite unable to offer any opinion as to the pro- 

 bable cause of these reversals, or as to how they were produced, beyond 

 stating the probability that, although there were many points of dif- 

 ference, they would be found to be in accordance with the generally 

 accepted theory worked out by Gapt. Abney, and were due more or less 

 to oxidation or rehalogenisation of the exposed parts of the film, and 

 that owing to the peculiar reducing action of the alkaline thio-car- 

 bamides the film during development was practically in the same state 

 as if it were over-exposed. It seemed also probable that sulphur was 

 the active agent in producing the reversals. 



