52 Ml'. Warington 071 the coloured Films 



of both systems and giving superior attention to the worst, if 

 written previously; and if otherwise, why is no reference 

 made to the treatise conducted with the common Roman no- 

 tation? These considerations are almost sufficient of them- 

 selves to throw a doubt on its genuineness, although we must 

 wait for the discovery of more direct evidence before any de- 

 finite conclusion is broached. I know not what the forth- 

 coming work of M. Chasles may contain, but every one in- 

 terested in these matters must be well aware how greatly we 

 are indebted to that able writer, and will readily leave the 

 discussion of this point in his hands. 



IX. On the coloured Films p7-odiiced by Electro-chemical Agency 

 and by Heat. By R. Warington, Esg.* 



'^r^HE following paper is intended as an answer to a memoir of 

 -*- the late Prof. Nobili on this subject, the translation of which 

 appeared in the first volume of the Scientific Memoirs, p. 94, 

 under the title of a " Memoir on colours in general, and par- 

 ticularly on a new chromatic scale deduced from metallo- 

 chromy for scientific and practical purposes." As this paper 

 contains a great detail of matter on the physical characters and 

 properties of colours and coloured films, and as it is only with 

 respect to the chemical part of the subject that I propose 

 treating it, it will be necessary to extract such sentences as 

 refer more immediately to the questions at issue. I should 

 not have ventured to attack a memoir coming from so 

 high an authority as Professor Nobili, but from its having as 

 yet elicited very little notice, and the views taken being so 

 startling to the chemist and so perfectly original, I am in- 

 duced to offer some practical experimental remarks on the 

 subject. The memoir naturally resolves itself into two distinct 

 subjects; namely, the nature of the coloured films produced 

 through the medium of electro-chemical agency ; and secondly, 

 those produced by means of heat; these it is my intention to 

 treat of separately and distinctly in their order. 



Professor Nobili dates his discovery of the electro-chemical 

 appearances as far back as the year 1826, and the account of 

 them was laid before the French Institute in November 1828, 

 and by their advice the distinctive appellation of metallo- 1 

 chromy was adopted. The method by which these appear 

 ances are produced is thus described, p. 94 : " A plate of 

 platina is laid horizontally at the bottom of a vessel made of 

 glass or china. A platina point is vertically suspended over 



* Communicated by the Author, 



