308 Mr, Faraday on M. PetitjearCs Silvering Process, [June 13, 



the half-dried mud of our streets without revealing to us more or 

 less of the features of this law. I would say, in conclusion, that 

 the spirit in which this problem has been attacked by geologists, 

 indicates the dawning of a new day for their science. The great 

 intellects who have laboured at geology, and who have raised it to 

 its present pitch of grandeur, were compelled to deal with the 

 subject in mass ; they had no time to look after details. But the 

 desire for more exact knowledge is increasing ; facts are flowing in, 

 which, while they leave untouched the intrinsic wonders of geology, 

 are gradually supplanting by solid truths the uncertain speculations 

 which beset the subject in its infancy. Geologists now aim to 

 imitate, as far as possible, the conditions of nature, and to produce 

 her results ; they are approaching more and more to the domain of 

 physics ; and I trust the day will soon come when we shall interlace 

 our friendly arms across the common boundary of our sciences, 

 and pursue our respective tasks in a spirit of mutual helpfulness, 

 encouraeement, and goodwill. 



[J.T.] 



WEEKLY EVENING MEETING, 

 Friday, June 13. 



SiE Roderick I. Murchison, G.C.S. F.R.S. Vice-President, 

 in the Chair. 



Professor Faraday, D.C.L. F.R.S. 



On M. Petitjea7i*s process for Silvering Glass : some Observations 

 on divided Gold. 



M. Petitjean's process consists essentially in the preparation of 

 a solution containing oxide of silver, ammonia, nitric, and tartaric 

 acids, able to deposit metallic silver either at common or somewhat 

 elevated temperatures ; and in the right application of this solution 

 to glass, either in the form of plates or vessels. 1540 grains of 

 nitrate of silver being treated with 955 grains of strong solution 

 of ammonia, and afterwards with 7700 grains of water, yields a 

 solution, to which when clear 170 grains of tartaric acid dissolved 

 in 680 grains of water is to be added, and then 152 cubic inches 

 more of water, with good agitation. When the liquid has settled, 

 the clear part is to be poured off; 152 cubic inches of water to be 



