376 Mr. J. Gill on the Dynamical Theory of Heat. 



gradually thrown into orbital courses which might continue 

 for a long time under the influence of planetary laws. Finally, 

 the effect of the resisting medium causes the sun's attraction 

 to preponderate more and more, and the great stream of meteoric 

 matter rolls on, gradually approaching the sun, in a vast spiral 

 vortex. As graphically imagined by Prof. "W. Thomson, " each 

 meteor thus goes on moving faster and faster, and getting 

 nearer and nearer the centre, until some time, very suddenly, it 

 gets so much entangled in the solar atmosphere as to begin to 

 lose velocity. In a few seconds more it is at rest on the sun's 

 surface, and the energy given up is vibrated across the district 

 where it was gathered during so many ages, ultimately to pene- 

 trate, as light, the remotest regions of space." It is supposed 

 that the principal store of energy which is to furnish future 

 sunlight is in the vis viva and the gravitating power of the 

 meteoric bodies at present circulating inside the earth's orbit, 

 and probably giving origin to the zodiacal light. However vast 

 these clouds of meteoric matter may be, analogy would certainly 

 indicate that their decrease from the fiery rain which they are 

 continually pouring down upon the sun should be made up from 

 some perennial source of supply, and also that some cosmical 

 process should prevent the continual growth of the sun's mass 

 which would result from the conditions of the meteoric theory 

 in its present apparently incomplete form. If the idea of the 

 volatilization of the meteoric matter from the sun's surface, and 

 its diffusion into space, does not involve any contradiction to 

 known physical laws, the system of solar meteorology which I 

 have endeavoured faintly to sketch would tend to show, 1st, that 

 a continuous supply of solid meteoric matter may be accounted 

 for ; 2ndly, that the'sun's mass may remain constant ; and 3rdly, 

 that the molecular motion of common matter, supposed by the 

 repulsion theory of thermo-dynamics to be directly inconver- 

 tible into work, may be converted into the force of gravitation 

 by the supposed phenomena of the meteoric theory ; and hence 

 would result strong presumptive evidence of a general stability of 

 equilibrium in all the physical phenomena of the universe. The 

 quantity of heat emanating from the sun is so vast that no phy- 

 sical theory of its replenishment can be considered satisfactory 

 which should not provide for an indefinite supply of heat-pro- 

 ducing material; and no physical theory can meet this require- 

 ment except on the principle of circulation and transformation. 

 And are not all natural analogies in favour of such a prin- 

 ciple ? 



However attractive such speculations may be to the fancy, I 

 should not choose to obtrude hypotheses of cosmical dynamics 

 unconnected with practical objects. In my long observations on 



