502 Mr. Gr. J. Stoney on the Solar Eclipse, August 1868. 



different phases of combustion occur, but also the temperatures 

 of ignition, depend upon the attraction which all the groups of 

 neighbouring atoms, and therefore even those which take no 

 part in the compound produced, exert upon each other. Every- 

 one knows that phosphorus begins first to unite with pure oxygen 

 at from 20° C. to 30° C. to form phosphorous acid, that a slight 

 addition of different hydrocarbons raises the temperature at 

 which combination begins to above 30° C, and, lastly, that by an 

 admixture of nitrogen the temperature at which the phosphorus 

 begins to emit light is lowered much below 20° C. 



It is scarcely necessary to remark here that the method which 

 has been described for the estimation of the temperature of the 

 flames of explosive gas-mixtures is applicable to those alone in 

 which only two elements enter into combustion, since we are not 

 in a position to indicate in more complicated cases which of the 

 different possible products of combustion has been formed during 

 the successive phases of the combustion. On the other hand, 

 by the aid of the subjoined formula we can calculate the tempe- 

 rature t } of the flames of explosive mixtures in which only two 

 elements are burned, when first we determine by experiment, 



171 



once for all, the coefficient -, made up of small whole numbers, 



n 



which represents the fraction of the whole gas-mixture which 

 is combustible within certain intervals of temperature, 



*,= - 



(11 + 0) + *, (l- I) H + * (l- ™)0 + <r q q 



In this formula the roman capital letters represent the atomic 

 weights of the gases burned together, a , cr v <r 2 , a q the specific 

 lieats of the single gases, and q the quantity by weight of any 

 incombustible gas which has been added, expressed in terms of 

 the unit employed in H and 0. 



LXVI. On the Sola?* Eclipse, August 1868. 

 By G. Johnstone Stoney, M.A., F.R.S.* 



IN May last I sent a memoir to the Royal Society on the Con- 

 stitution of the Atmospheres of the Sun and Stars, which 

 contained, in an Appendix, suggestions relative to observations 

 of much interest which might be made during the eclipse of 



* From the Monthly Notices of the Royal Astronomical Society, De- 

 cember 13, 1867. 



