366 , Miscellaneous Intelligence. 



In the first series, where three or four colours may be distin- 

 guished, the yellow and purple increase in intensity, from the 

 exterior to the interior ; but the blue and the green decrease in 

 intensity, in the same direction. The oxide of the central spot 

 commences immediately upon the edge of the colour of the last 

 series. 



Deductions. — These results shew the strong analogy between 

 the systems of colours produced by heat on metals in contact 

 widi the air, and those reflected by thin plates described by 

 Newton. This point admits of farther research, and it is pro- 

 bable the size of the coloured zones or metals will follow the 

 same law of decrement found to obtain with the coloured rings 

 produced by object glasses. 



This analogy induces the supposition that, in the combination 

 of oxygen with the surface of the heated plate of metal, a thin 

 pellucid coat of oxide is formed, diminishing in thickness as it 

 recedes from the centre of the heat, as indicated, indeed, by the 

 distribution of the observed colours. This idea leaves nothing 

 mysterious in the appearance of these phenomena, except that 

 belonging to these plates generally, and their manner of pro- 

 ducing these particular effects. On this point nothing better 

 than the hypothesis of Newton has, since his time been advanced. 



The action of heat is not sufficient to produce these pheno- 

 mena ; the access of oxygen, which may combine with the metal 

 chemically, is required. This may give rise to the query, 

 whether oxygen has not a general influence in the production of 

 such effects. It has certainly been proved that, when a reflectipn 

 of these colours, in this order, is obtained, that reflection is occa- 

 sioned by thin plates ; but the inverse of this proposition, namely, 

 that whenever thin plates are formed, these colours, in this 

 order, are reflected, has not been proved ; and there are, indeed, 

 even arguments to support the contrary ; as, for instance, the 

 bubbles of various solutions, which, though very thin and lasting, 

 do not give any appearance of colour. 



Giornale di Fisica, II. p. 145. 



