On the Temperature of Incandescence. 225 



Siemens,' Mr. Williams" and M. Violle," the assumption that 

 the known constituents of the sun must be wholly gaseous, 

 will, in so far as temperature is concerned, be no longer neces- 

 sary, and the idea that it is a sphere of fused material, such 

 as originally constituted our melted earth, or such as is now 

 ejected by terrestrial volcanoes, will be quite admissible ; and 

 it seems to me that the experiments I have herein apparently 

 correlated will then account for its dark interior. For, assum- 

 ing it to be a perfectly limpid fused globe, like many a blow-pipe 

 bead at about that temperature, covered with a crust of less fusi- 

 ble or incompatible material, crystallizing out from the mass, as 

 feldspar and hornblende perhaps crystallized out from granite, 

 or a crust of the same material reduced to a pasty or opaque 

 condition upon the surface, by the chill of its radiation into sur- 

 rounding space, the great luminosity of the crust would be per- 

 fectly consistent with its temperature, whether the same as that 

 of the sun or lower, and the predicated phenomena of its surface 

 would almost precisely accord with those actually observed. In- 

 ternal convective disturbances and general equilibrium currents 

 of the crust, in large areas, by whatever cause produced, should 

 give rise, — the first to the production of the willow -leaves, facu- 

 las, and spots, — and the latter, to their actual translation over 

 the sun's surface. Every little local depression of the pasty 

 crust would cause a slight local exudation of the interior transpa- 

 rent lava, which would chill by radiation, become opaque and 

 brightly luminous, and then gradually retrograde to a condition 

 of incandescence determined by the general temperature of the 

 surface, and where especially violent local disturbances, such as 

 gaseous eruptions, might break away or part the crust, there the 

 interior would seem, as it actually would be, non-luminous or 

 dark. 



The common assumption that the red protuberances or so- 

 called hydrogen flames are of the nature of flames, and consist 

 of hydrogen gas at a temperature enormously high, I am dis- 

 posed to question, for I am unable so far to find the evidence of 



4 Siemens, Dr. C. W. Solar Physics. Lecture at the Royal Institution. April 27, 1873. 

 Nature, Vol. 28, p, 19. 



5 Williams, W. Mattieu. Fuel of the Sun. Humboldt Library, No. 41, p. 215. 



6 Compte Rendus, Vol. LXXVIII, pp. 186 and 1425, 



