281 



The principal object of this paper is to prove that most combustible 

 bodies undergo a kind of combustion, attended with light and heat, 

 at a temperature considerably below that usually assigned as their 

 point of ignition. This fact has been already noticed with regard to 

 phosphorus and sulphur ; and the pale blue flame produced in the 

 vapour of ether by a hot palladium or platina wire, before the wire 

 itself becomes vividly ignited, is another instance of the same general 

 law, which the author finds applicable to all compound, and a few of 

 the simple inflammable bodies. Of these he gives a variety of exam- 

 ples among oleaginous, resinous, and carbonaceous products, both 

 animal and vegetable, which, when thrown on a hot iron, exhibit a 

 pale and faintly luminous flame. Those on the other hand which are 

 very volatile, such as camphor, the essential oils, ether and alcohol, 

 rise in vapour before they reach the temperature necessary for their 

 combustion ; but they may be made to exhibit the same phenomena, 

 by directing their vapour against a body heated below redness. The 

 contact of pure oxygen gas immediately heightens the intensity of 

 the light and heat evolved on these occasions, and excites them into 

 a more decided and vivid combustion. 



The author next adverts to the nature of the products of this low 

 form of combustion, which, in organic substances, appear to him to 

 form an intermediate link between those of open combustion, and 

 those of fermentation and putrefaction. He considers the phenomena 

 he has described as confirming the truth of a law he formerly an- 

 nounced, namely, that " the evolution of heat during chemical change 

 is, cceteris paribus, proportionate to the degree of change from iso- 

 lation, or weak combination, towards firm and simple union." He 

 thinks they will afford an explanation of many cases of spontaneous 

 combustion, which have hitherto been involved in mystery j such as 

 that of porous combustible matters, as oily cotton, tow, or wool, when 

 accumulated in considerable quantities, in places protected from cool- 

 ing, or where air has limited access; and also of heaps of coal or 

 charcoal, of pyrophori and pyrites j and the same principles may per- 

 haps also account for the phenomena of the spontaneous combustion 

 of the human body which are on record. 



May 8th, 1834. 

 FRANCIS BAILY, Esq., Vice-President, in the Chair. 



A paper was read, entitled, " On the Connexion between Re- 

 fracted and Diffracted Light." Bv Paul Cooper, Esq, Communi- 

 cated by J. G. Children, Esq., Sec.'R.S. 



The purport of the present paper, as stated by the author, is to con- 

 nect the phenomena of the dispersion of light arising from refraction, 

 with that consequent upon diffraction, by showing, 1st, "that white 

 refracted light is formed by the superposition of fringes of colours, or 

 rays of light uniformly refracted, which compensate each other in suc- 

 cession j 2nd, that diffracted white light is formed by the superpo- 



