1868.] 



Constitution of the Sun and Stan 



37 



dence or the descending currents of convection. Here, then, if this sub- 

 stance be in sufficient abundance, we have all the conditions necessary for 

 the sun's luminous clouds. And we are led almost irresistibly to conjec- 

 ture that in carbon* we have such a substance. The mass of its molecules 

 is very low, either six, or twelve, or twenty-four times the mass of a mole- 

 cule of hydrogen. It appears to have just the requisite degree of fixed- 

 ness ; it shows no sign of volatility at any ordinary high temperature, but 

 has been driven into vapour by one hundred elements of Bunsen's battery, 

 each element consisting of six ordinary cells coupled side by side ; that is 

 at a temperature which may, quite consistently with everything we know, 

 be that of the strata adjoining the sun's photosphere. There is enough of 

 carbon in the sun to produce the luminous clouds, if carbon be as large a 

 constituent of the sun as it is of the earth ; and most of the carbon in the 

 sun is probably uncombined, as carbon does not seem apt to form com- 

 pounds likely to be abundant which can stand intense heat. It is, moreover, 

 precipitated from its vapour as a black body with the most perfect power 

 of emission of any known substance ; and we are assured that the luminous 

 clouds consist of some such material by the absence of bright lines from 

 the solar spectrum. It would probably be impossible, in the present state 

 of our knowledge, to put forward on behalf of any other substance, 

 simple or compound, anything like the same claim to be deemed the mate- 

 rial of which the luminous clouds consist. And I know of but one consi- 

 deration to be set on the other side, viz. that if the luminous clouds be a 

 smoke of carbon, and if the rain beneath is more properly to be described 

 as a fall of soot, in flakes like snow, and if these flakes come to rest 

 upon the surface of an ocean beneath, they must by their high radia- 

 ting power render this surface eminently luminous, which we know from 

 the phenomena of spots that it is not. 



63. As, then, there are strong reasons for surmising that the lumi- 

 nous clouds consist of carbon, we are led to enquire what may exist to 

 remove the one difficulty in which this hypothesis involves us. Now, in 

 the first place, it would disappear if the heat in the space beneath the 

 clouds melts the falling flakes, so that they reach the ocean like rain, 

 and mix with the other liquids constituting it. And it would disappear 

 if the heat and dryness of the space beneath the clouds enable it to 

 evaporate the flakes ere they reach the ocean. And, finally, it would dis- 

 appear if there be no such ocean, but only a continuation of the atmosphere 

 becoming denser and hotter. It will be necessary to examine this last 

 hypothesis with some care to see that it is compatible with the known phe- 

 nomena of spots. 



64. It is not likely that carbon is the only substance in the sun that 



* In connexion with Dr. Frankland's discoveries respecting flame, it should not be 

 forgotten that such solid particles as Davy supposed in flame are undoubtedly adequate 

 to produce luminous effects, and possibly are a source of light in other cases as well as 

 on the sun. 



