Mr. J. Phillips on Ancient Metallurgy and Mining, 247 



All writers on the casting of specula, including Lord Ox- 

 mantown in the second volume of the same series of the 

 Edinburgh Journal of Science, had received or prescribed 

 annealing as the course to be used in the casting of the metal ; 

 but in spite of all precautions, when the metal was of the best 

 proportions of copper and tin for colour and polish, the cast- 

 ingswere continually found to be cracked, and not unfrequently 

 broken into fragments at the termination of the annealing 

 process, whilst the metal was often so brittle as not to bear 

 grinding with emery without tearing up. 



In this state of the subject I undertook an experiment in the 

 contrary direction (see page 18 of the paper referred to), and 

 cast a metal upon a chilling surface, when I found that I had 

 obtained by it the great desideratum, a hard compact metal, 

 which bore grinding and polishing admirably. I repeated the 

 experiment several times with small mirrors, and obtained 

 always the same result. Having obtained full confidence in 

 the method, I recommended it to Lord Oxmantown's notice 

 in the before-named paper. 



This chilling process in casting, and my method of making 

 the polishing powder, detailed in the same paper, by precipi- 

 tating with ammonia an oxide of iron from a solution of the 

 sulphate and then calcining, will, 1 am sure, in future time be 

 accounted amongst the most important discoveries connected 

 with the construction of the reflecting telescope, and I claim 

 the discovery and first publication of them. 

 I am, Gentlemen, 



Your obedient Servant, 



University College, March 13, 1849. RiCHARU PoTTEB, A.M. 



XXXV. Thoughts on Anciejit Metallurgy and Mining in Bri- 

 gantia, and other parts of Britain, suggested hy a page of 

 Pliny's Natural History, By John Phillips, Esq., F.R.S.f 

 F.G.S* 



TO one who meditates on the progress of natural know- 

 ledge, the difficulty of penetrating to a true estimate of 

 its condition in past ages often appears unconquerable, except 

 in cases which admit of the interpretation of ancient results 

 by modern laws and theories. Once in firm possession of 

 such laws, we enclose the old phaenomena, so to speak, in a 

 field to which are only such and such possible avenues, and 



* From the Proceedings of the Yorkshire Philosophical Society for 

 March 1848. 



