Mechanical Energies of the Solar System. 427 



the sun's disc are probably due to eddies which must be con- 

 tinually produced throughout the atmosphere of intense resist- 

 ance between his surface (which at the equator revolves only at 

 the rate of 1*3 mile per second) and the great vortex of mete- 

 oric vapour, which a few miles outside revolves at the rate of 

 277 miles per second about the equatorial regions, and (if not 

 at the same) certainly at enormously great rates a few miles 

 from the sun's surface in other localities. Such eddies may 

 ordinarily be seen as the streaks which have been compared to 

 ''the streamers of our northern lights'' (Herschel, § 387), and 

 when any one of them sends a root down to the sun's surface it 

 may cause one of the " minute dark dots or pores " which have 

 been observed, and which, when attentively watched, are found 

 to be always changing in appearance (Herschel). A great rota- 

 tory storm, like the tropical hurricanes in the earth's atmosphere, 

 may occasionally result from smaller eddies accidentally com- 

 bining, or from some disturbing cause originating at once an 

 eddy on a much larger scale than usual, and may traverse the 

 sun's surface, preventing the distillation of meteoric vapour 

 over a great area, and consequently checking both the supply of 

 dynamical energy for radiant heat in the luminous atmosphere 

 of resistance, and the torrents of condensed meteoric vapours 

 falling to the surface below it. The consequence would be, that 

 the meteoric rain (Herschel's " cloudy stratum") would be 

 cleared away for a certain space under the central parts of the 

 storm by falling down to the liquid or solid surface, and the 

 luminous atmosphere would lose intensity over a larger space 

 bounded very irregularly by a region of minor eddies, which 

 would cause varying streaks of light. These are exactly the 

 circumstances assumed by Sir William Herschel to account for 

 the great spots with their dark centres surrounded by sharply 

 terminated penumbrse inside the abrupt ragged boundaries of 

 the bright surface, and the branching luminous streaks or 

 *' faculse" in the bright surface outside in their neighbourhood. 

 (Sir John Herschel's Astronomy, § 388.) 



No. IV. (Added August 15, 1854.) On the Age of the Sun. 



The moment of the sun's rotatory motion (according to the 

 hypothesis mentioned above in the "Explanation of the Tables" 

 regarding the moment of inertia of his mass) is one-third of his 

 mass multiplied by his radius, multiplied by the linear velocity 

 of his equator, and is therefore equal to that of a planet at his 



1*27 1 



surface having a mass equal to ^ — 977 ~fi^ ^^ ^^^ ^^^ mass. 



This is equal to the quantity of meteoric matter which would 

 fall in during 25,000 years, at the present rate ; and therefore 



2F2 



