MECHANICAL ENERGIES OF THE SOLAR SYSTEM. 7o 



To test this conclusion for the case of the earth, let T" denote the number of re- 

 volutions round the Sun in the time T. Then, if the unit in which T is measured 

 be the time of a revolution with the angular velocity n r , we have 



rrv m J- 



32,400,000. 



Thus, if T be 4000 years, we have 



T , 4000 _ 16,000,000 39m 

 32,400,000 2 



or only 3999 \ actual years in a period of 4000 times the present year. Similarly, 

 we should find a loss of | of a year on a period of 2000 years ago ; that is, of 

 about a month and a-half since the Christian era. Thus, if we reckon back about 

 2000 times the number of days at present in the year, we should find seasons, 

 new and full moons, and eclipses, a month and a half later than would be if the 

 year had been constantly what it is. Now we have abundant historical evidence 

 that there is no such dislocation as this, either in the seasons, or in the lunar 

 phenomena ; and it follows that the central attracting mass of the solar system 

 does not receive the augmentation required by the extra-planetary meteoric 

 theory of solar heat. But the reasoning in the preceding paper establishes, with 

 very great probability, a meteoric theory of Solar Heat ; and we may therefore 

 conclude that the meteors supplying the Sun with heat have been for thousands 

 of years far within the Earth's orbit. 



No. II. Friction between Vortices of Meteoric Vapour and the Sun's Atmosphere the 



immediate Cause of Solar Heat. 



It has been shown that the meteors which contribute the energy for Solar Heat 

 must be for thousands of years within the Earth's orbit before falling to the Sun. 

 But a meteor could not remain for half a year there, unless it were revolving round 

 the Sun, with at each instant the elements of a circular or elliptic orbit. Hence, 

 meteors, on their way in to the Sun, must revolve, each thousands of times round 

 him, in orbits which, whatever may have been their primitive eccentricities, must 

 tend to become more and more nearly circular as they become smaller by the 

 effects of the resisting medium. The resistance must be excessively small, even 

 very near the Sun ; since a body of such tenuity as a comet, darting at the rate 

 of 365 miles per second within one-seventh of his radius from his surface, comes 

 away without sensible loss of energy. If, as is probable, the atmosphere of that 

 part of space is carried in a vortex round the Sun by the meteors and other 

 planets, it may be revolving at nearly the same rates as these bodies at different 

 distances in the principal plane of the solar system ; but we cannot conceive it 

 to be revolving in any locality more rapidly than a planet at the same distance. 



VOL. XXI. PART I. X 



