46 



Mr. G. J. Stoney on tlie Physical 



[Recess, 



the semiaxis major is 4* 98 times that of the earth's orbit. The perihelion 

 distance must be very small (say, 0*01) to admit of the swarm's grazing the 

 sun's atmosphere at each perihelion passage. This would assign 9*95 to 

 the aphelion distance, a quantity from which it cannot much deviate. Now 

 the mean distance of Saturn is 9*54 ; so that we may safely conclude, if the 

 explanation which is now offered is the correct one, that the meteorites in 

 question were diverted into the solar system, by either Jupiter or Saturn, 

 at no enormously remote period ; just as the November meteors seem to 

 have been brought in by the attraction of the planet Uranus in a.d. 126. 

 At each perihelion passage some of the outlying members of the stream 

 become entangled in the upper parts of the sun's atmosphere, dashing 

 through it at a rate of about 414 kilometres per second*. The enormous 

 friction they must undergo before they are brought to a state of relative 

 rest will convert their immense vis viva into heat, which will be expended 

 in raising the temperature of the upper strata of the part of the sun's at- 

 mosphere upon which they act. This part is of necessity more equatorial 

 than polar, and is very much more equatorial than polar, except on the pe- 

 culiar supposition, which we have no reason to select, that the plane in 

 which the meteors move is very nearly perpendicular to the plane of the 

 sun's equator. The heat imparted by the meteors to the sun's atmosphere 

 therefore tends to diminish that defect of temperature in the upper parts 

 at the equator which occasions the trade- winds of the sun. The influx of 

 meteors, therefore, into the sun's atmosphere mitigates the violence of the 

 trade-winds, and in this way enfeebles the cause of cyclones and of spots. 

 Furthermore, except on the very improbable hypothesis that the axis-major 

 of the orbit of the meteors lies exactly along the line of intersection of its 

 plane with that of the sun's equator, the meteors must act more on one 

 side of the equator than the other, and thus soften the trade-winds, and 

 render the spots less frequent and extensive in one hemisphere than in 

 the other. So that the hypothesis of a stream of meteors has the follow- 

 ing points in its favour : — it is a vera causa ; it accounts for two wholly 

 distinct phenomena, the periodicity of the spots and their prevalence in one 

 hemisphere more than in the othert ; and it leads to such an aphelion dis- 



* The velocity of the sun's equator is about 2 kilometres per second. 



f [It also accounts for the approach of the zones of spots to the equator during the pex-iods 

 of minimum spot-frequency ; inasmuch as when the current descending at the equator from 

 great altitudes is enfeebled, the surface winds of middle latitudes, which have a tendency 

 to cling to the photosphere, owing to their having a less rotation, will encroach further upon 

 the equatorial current and will thus bring the junction between them, along which the spots 

 lie, nearer to the equator. 



If the decennial mutations of the spots be due to a current of meteors, this hypothesis 

 ought to offer some indication of the cause of fluctuations of longer period, such as that 

 of fifty-six years. This is perhaps to be sought in the great perturbation which the 

 motion of the members of the stream must suffer from the attraction of Jupiter. This 

 planet must act upon them with intense effect, since the planet and the meteors have 

 nearly the same periodic time. — July 1868.] 



