MECHANICAL ENERGIES OF THE SOLAR SYSTEM. 79 



tangential velocity of this vortex immediately external to the radiant region of in- 

 tense resistance may be found to be, in all solar latitudes, very nearly that of a planet 

 close to the Sun. If it be so, the moment of the motion communicated to the Sun 



314159 

 by any mass of meteoric matter will be 4 of what would be communi- 



cated by the incorporation of an equatorial planet of equal mass : as much as 5^ 

 of the Sun's mass would have to fall in to produce his present rotation : and 

 32,000 years would be the time in which this would take place, at the present rate 

 of meteoric incorporation as estimated above. 



It will be a very interesting hydrodynamical problem, to fully investigate the 

 motion of the meteoric vortex ; and among results to be derived from it will be 

 strict estimates of the contribution to the Sun's rotatory motion, and of the quan- 

 tity of heat generated, by any amount of meteoric matter in becoming incorporated. 

 With these, and with an accurate determination of the rate at which the Sun ra- 

 diates heat, we should be able to fix, with certainty, the augmentation of his 

 velocity of rotation actually taking place at present from year to year, and to 

 estimate the time during which the existing rotation would be acquired by me- 

 teoric incorporation going on always at the present rate and in the present man- 

 ner. Whatever this time (which I shall call T years, to avoid circumlocution 

 below) may be, it probably will not be found to differ very widely from the pre- 

 ceding estimate of 32,000 years. 



Now, from the fact that the Sun's equator, the planets' orbits, and the Zodia- 

 cal Light, all lie nearly in one plane, it appears highly probable that the Sun's 

 present motion has really been acquired by the incorporation of meteors. It is 

 certain that the present manner and rate of meteoric action cannot have been 

 going on for more than the indicated period (T), without giving the Sun a greater 

 rotatory motion than he has, unless (which is very improbable) he were previously 

 rotating in a contrary direction round the same axis : and, at only the present 

 rate, it cannot have been going on for less than that time, unless the Sun has 

 been created with a rotatory motion round his present axis, or has acquired such 

 a motion from some independent mechanical action. The actual rate of Solar 

 radiation in time past may, for all we now know, have been sometimes much 

 greater and sometimes much less than at present ; and there probably has been 

 a time before, when meteors in abundance fell direct to the Sun from extra- 

 planetary space, some getting stopped on their way by the Earth, and illuminating 

 it by friction in its atmosphere and impact at its surface. But the kind of me- 

 teoric action now going on, has in all probability produced neither more nor less 

 than T times the quantity of heat now emitted from the Sun in one year. All 

 things considered, it seems not improbable that the Earth has been efficiently illu- 

 minated by the Sun alone for not many times more or less than 32,000 years. 

 As for the future, it will be a most interesting problem to determine the mass 



VOL. XXI. PART I. Y 



