[ n ] 



II. Summary Considerations vpon variegated Colours of 

 Bodies when reduced into thin Pellicles ; to which is added 

 ah Explanation of the Colours of tempered Steel, and of 

 those of Peacocks' Feathers, Extracted from a IVork on 

 Colours; by C. A. Prieur. 



[Concluded from p. S09.] 



X SHALL conclude with some observations upon two kinds 

 of curious phasnomena analogous to my subject, and of 

 which I think myself warranted in giving an explanation 

 different from that generally admitted. 



The first subject I allude to chiefly concerns the colours 

 of tempered steel. 



Newton has ranked them among those dependent upon 

 coloured rings, not from any special examination, but by 

 a simple consequence of the system he founded, and sup- 

 posing that the metallic particles must change in their size 

 from the action of the fire *. Beyond this he did not look, 

 in order to ascertain if there were other causes to take into 

 the account. 



Some more recent inquirers, on the contrary, have, with- 

 out hesitation, attributed these colours to a varied denree of 

 oxidation t, because they thought they saw a great simili- 

 tude between the appearances in question and those of se- 

 veral metals placed in circumstances in which they were in 

 fact oxidated. This subject at least merits a closer exa- 

 mination, and I adopted the following simple method to 

 elucidate it. 



I placed a steel watch-spring in the flame of a candle, and 

 heated it for a few minutes in a fixed position. Havin<T 

 afterwards taken it out, I found, upon cooling and wiping 

 it, that there was to the right and left of the central point, 

 where the flame had acted, a series of coloured gradations 

 with periodical returns, such as would have been exhibited 



* Optics, book ii. part 3. prop. 7. 



f Independently of several authors who have adopted this prejudice with 

 respect to oxidation, we tee it exhibited, in a recent publication, full of inter- 

 esting views and observations, with the exception of this doctrine alone. See 

 in Nicholson's Journal for June ISOO, a report upon fine cutlery, 



1 by 



