TEANSACTIONS Or THE SECTIONS. 61 



(1) Guyton and Daniell, Prinsep, &c. — Expansion of Solids and Gases. 



(2) Draper. — Refrangibility of Lig-ht. 



(3) Clement and Desormes, Deville. — Specific Heat. 



(4) Becquerel, Siemens. — Thermo-electricity and Electric Conductivity. 



(5) Bunsen, Zollner. — Explosive Power of Gases. 



(6) Newton, Waterston, Ericsson, Secchi. — Radiation. 



(7) Thomson, Helmholtz. — Mechanical Equivalent of Heat. 



(8) Deville Debray. — Dissociation. 



After treating of the great disparity of opinion regarding the temperatui'c of the 

 sun, the author proceeds to detail how it is possible, from the known luminous 

 intensity of the sim, to derive a new estimate of solar temperature. This calculation 

 is based on a definite law relating to temperature aud luminosity in the case of solids, 

 viz. the total luminous intensity is a parabolic function of the temperature above 

 that temperature where all kinds of luminous rays occur ; so that if T is a certain 

 initial temperature, and I its luminous intensity, a a certain increment of temperature, 

 then we have the following relation : — 



T+M(a)=?*2l. 



The temperature T is so high as to include aU kinds of luminous rays, viz. DiX)' C, 

 and the increment a is 46° C. This formula expresses well the results of Draper, 

 and his numbers are used as a first approximation. It results from the above 

 equation that, at a temperature of 2400° C, the total luminous intensity will be 900 

 times that which it was at 1037° C. Now the temperature of the oxy hydrogen 

 fiame does not exceed 2400° C, and we know from Fizeau and Foucault's experiments 

 that sunlight has 150 times the luminous intensity of the lime-light ; so that we 

 only require to calculate at what temperature this intensity is reached in order to 

 get the solar temperature. This temperature is 16000° C, in round numbers. 

 Enormously high temperatures are not required, therefore, to produce great luminous 

 intensities, and the temperature of the sun need not, at least, exceed the above 

 number. Sir William Thomson, in his celebrated article, " On the Age of the Sun's 

 Heat," says, " It is almost certain that the sun's mean temperature is even now as 

 high as 14000° C. ; " and this is the estimate with which the luminous intensity 

 calculation agrees well. 



On the Temperature of the Electric SjoarJc. By James Dewak, F.R.S.E. 



The author begins this paper by calculating the highest hypothetical tempera- 

 ture that could be produced by the chemical combination of the most energetic 

 elements if all the heat evolved could be thrown into the product. This would 

 not exceed 19.j00° C. in the case of silica, and 15000° C. in the oxides of alu- 

 minium and magnesium ; aud these .are the highest results. The estimation of the 

 temperature of the electric spark is based on the thermal value of each spark, 

 together with the volume of the same. The methods of observing these quantities 

 are fully detailed in the memoir. The general result -may be stated thus, the tem- 

 perature of the electric spark used in the experiments ranged between 10000° C. 

 and 15000° C. 



On the Stresses produced in an Elastic Solid hij Inequalities of Temperature. 



By S. HoPKiNSON, B.Sc. * 



Since the equations of equilibrium aud the equations connecting strains and 

 stresses in an elastic solid are both line,ar, the principle of superposition holds ; and 

 we may consider the effect of each cause tending to produce stress as if none other 

 existed, and finally add the result of the separate causes to obtain the effect of all 

 acting together. 



It is foimd that the effect of imequal heating is to subtract from the components of 



lateral force X, Y, Z, at any point, terms y-Tjy -I,y -I, where y is a constant 



QtX dy M(5 



