390 



Dr. C. W. Siemens. 



[Mar. 2, 



upon us how this great loss can be sustained without producing an 

 observable diminution of solar temperature even within a human 

 lifetime. 



Amongst the ingenious hypotheses intended to account for a con- 

 tinuance of solar heat is that of shrinkage, or gradual reduction of the 

 sun's volume suggested by Helmholtz. It may, however, be urged 

 against this theory that the heat so produced would be liberated 

 throughout his mass, and would have to be brought to the surface by 

 conduction, aided perhaps by convection ; but we know of no 

 material of sufficient conductivity to transmit anything approaching 

 the amount of heat lost by radiation. 



Chemical action between the constituent parts of the sun has also 

 been suggested ; but here again we are met by the difficulty that the 

 products of such combination would ere this have accumulated on the 

 surface, and would have formed a barrier against further action. 



These difficulties led Sir William Thomson to the suggestion that 

 the cause of maintenance of solar temperature might be found in the 

 circumstance of meteorolites falling upon the sun, not from great 

 distances in space, as had been suggested by Mayer and Waterston, but 

 from narrow orbits which slowly contracted by resistance until at last 

 the meteorolites became entangled in the sun's atmosphere and fell in ; 

 and he shows that each pound of matter so imparted would represent 

 a large number of heat units without disturbing the planetary equili- 

 brium. But in considering more fully the enormous amount of 

 planetary matter that would be required for the maintenance of the 

 solar temperature, Sir William Thomson soon abandoned this hypo- 

 thesis for that of simple transfer of heat from the interior of a fluid 

 sun to the surface by means of convection currents, which latter hypo- 

 thesis appears at the present time to be also supported by Professor 

 Stokes and other leading physicists. 



But if either of these hypotheses could be proved, we should only 

 have the satisfaction of knowing that the solar waste of energy by 

 dissipation into space was not dependent entirely upon loss of his 

 sensible heat, but that his existence as a luminary would be prolonged 

 by calling into requisition a limited, though may be large, store of 

 energy in the form of separated matter. The true solution of the 

 problem will be furnished by a theory, according to which radiant 

 energy which is now supposed to be dissipated into space and irre- 

 coverably lost to our solar system, could be arrested, wholly or partly, 

 and brought back in another form to the sun himself, there to continue 

 the work of solar radiation. 



Some years ago it occurred to me that such a solution of the solar 

 problem might not lie beyond the bounds of possibility, and although I 

 cannot claim intimate acquaintance with the intricacies of solar 

 physics, I have watched its progress, and have engaged also in some 



