412 REPORT—1868. 
Meteors which penetrate the atmosphere are deflected downwards ; and the 
apparent position of their radiant-point is deflected upwards to an extent 
depending on its zenith-distance, by the same cause, termed by Prof. Schia- 
parelli the zenithal attraction—which follows a law very similar to that of 
atmospheric refraction, in displacing the apparent position of the radiant- 
point upwards, towards the observer’s zenith. The apparent displacement 
disappears at the zenith, and reaches its greatest value at the horizon, where 
it may amount in extreme cases to 17° 20'; so that a radiant-point may 
change its apparent place in the sky (from the effects of the earth’s attrac- 
tion alone) 34° 40' in twelve hours, between the times of its rising above the 
horizon in the east point and setting below it in the west. A correction for 
zenithal attraction is therefore necessary to be applied to the observed posi- 
tions of all radiant-points whose elongation is greater than 90° from the apex 
of the earth’s way; and formule for its calculation, in every case, are given 
at pp. 56, 57 of the memoir. 
The seventh chapter gives an account of the perturbations produced by 
the earth and the other planets on meteoric swarms with which they 
come in contact, or which pass in their immediate neighbourhood. Meteors 
moving in parabolic orbits, which overtake the earth with the least possible 
relative velocity, may, under the most favourable circumstances, be diverted 
into ellipses of periodic times varying from 4} to 120 years or upwards, 
according as they just graze the earth’s atmosphere, or pass at a distance of 
ten or more earth’s radii from its centre. The greatest effect, however, of 
the earth’s attraction on meteors of the November shower is no greater than 
would alter their periodic time from its present value to 28°67, or to 49-92 
years in opposite cases. Since such effects can rarely accumulate, the No- 
vember meteors can never be diverted into open orbits by the earth’s attrac- 
tion, but will continue to circulate in ellipses, intersecting the earth’s orbit, 
as at present, with little variation, about the earth’s place on the 14th of 
November. 
With regard to their introduction into the solar system, it is shown that, 
on account of the very small difference (;7,4 part of the whole) which must 
exist between the semiaxes major of the foremost and rearmost members of 
the meteoric group, supposing it to have reached its present extension in its 
orbit since the year a.p, 902, its actual diameter, if introduced into the 
solar system by the planet Uranus, could not have exceeded 168 miles. 
Should its diameter before encountering Uranus have been as much as 600 
miles, it must have revolved previously in an ellipse with a periodic time of 
not more than fifty years, which is as inconceivable as that it should have 
always continued to revolve without any disturbance in its present course. 
Should the planets Jupiter or Saturn have effected a diversion of the group 
from along elliptic or parabolic orbit into its present path, the possible 
limits of its original dimensions are much wider, but are still confined to a 
few earth’s radii, supposing that the present track of the group could have 
brought them sufficiently near to those planets to fall within the extreme 
boundaries of their attractions—that is to say, within 10:19 radii of the 
globe of Saturn from its centre, or within 27:27 radii from the centre of the 
planet Jupiter. The results of this chapter accordingly tend to confirm the 
opinion urged by Faye*, that the group of the November meteors must have 
originally formed part of the nucleus of Tempel’s comet. 
The eighth chapter treats of the transformation of materials occupying the 
celestial spaces into meteoric currents. The hypothesis of Sir W. Herschel 
* Comptes Rendus, vol. liv. p. 553 e¢ seq. 
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