242 



or heat must be generated by chemical action (combustion), or heat 

 must be generated by other forces than those of chemical action, 

 that is, by forces of moving masses. Any store of primitive heat 

 that can be drawn upon in solar radiation, must be entirely within the 

 sun. It is shown that such a store would almost certainly be in- 

 sufficient for the supply of the heat which has certainly been emitted 

 during 6000 years, and it is also shown with about equally strong 

 probability, that chemical action among elements of the sun's mass, 

 would be insufficient to supply the actual emission for any such 

 period of time. It is concluded that the source drawn upon in solar 

 radiation cannot be primitive heat, nor heat of intrinsic combustion. 

 If not heat of combustion at all, it must clearly be heat derived from 

 the motion of bodies coming to the sun (the utter insufficiency, in 

 point of duration, of ordinary motions of matter within the sun, 

 being quite obvious) ; or if it be heat of combustion, fuel must be 

 supplied from without. But no matter can come to the sun from 

 external space, without generating, from its motion alone, thousands 

 of times as much heat as it could possibly give rise to either by 

 combustion among elements of its own, or by combination with sub- 

 stances primitively in the sun, unless it were possessed of incompa- 

 rably greater chemical affinities than any known terrestrial or me- 

 teoric substance. It is infei'red that the source of solar heat must 

 be meteoric, and is the motion of meteors coming to the sun. The 

 idea that solar heat is so produced, appears to have been first pub- 

 lished by Mr Waterston, who brought it forward at the late meeting 

 of the British Association at Hull. 



But if (as was assumed by Mr Waterston) enough of meteors to 

 generate heat at the actual rate of solar radiation, were falling in 

 from extra-planetary space, the earth in crossing their path, would 

 be struck much more copiously by meteors than there is any pro- 

 bability it is ; and the increase of matter round the centre of the 

 system, would within the last two or three thousand years, have 

 caused an accelex'ation of the earth's motion, which history disproves. 

 Hence the meteors which supply the sun with heat must, at least 

 during historical periods, have been within the earth's orbit. We 

 see them there in the sunshine (when the sun himself is below our 

 horizon) a toi'nado of dust, called " the Zodiacal Light " whirling 

 round the sun and carrying the inter-planetary atmosphere with 

 them, probably to such an extent, as to cause centrifugal force 



