410 REPORT—1868. 
No trace of conformity to the ecliptic, or other signs of connexion of the 
radiant-points with each other or with great circles of the sky, can be de- 
tected, which would materially facilitate precise calculation of the diurnal 
and annual variations, if certain other elements of abundance of the meteors 
of particular showers were satisfactorily determined. 
Allowing for the effects of the earth’s velocity in its orbit, in assembling 
the apparent positions of the radiant-points of shower-meteors about that 
point of the ecliptic towards which the earth moves, and for the greater 
chances of vision of small comets when moving in direct orbits nearly coin- 
ciding with the ecliptic plane, than of those whose orbits are more inclined, 
or retrograde, Prof. Schiaparelli considers that both comets and meteors 
are distributed without any preponderance towards the plane of the ecliptic, 
and that they exhibit no prevailing tendency towards a direct rather than 
towards a retrograde motion in their orbits. 
The real mean velocity of shooting-stars may be determined from that of 
comets in their orbits, at their points of intersection with the orbit of the 
earth, which is 25°70 B. S. miles per second; while that of the earth in its 
orbit is only 18:18 miles per second*, Adding and subtracting these num- 
bers, the greatest and least mean relative velocities of meteors which en- 
counter the earth (respectively, moving to meet it directly, or to overtake it), 
no account being taken of the earth’s attraction, are 43°88 and 7:52 miles 
per second. The effect of the earth’s attraction is greater in the latter case 
than in the former (in the proportion of 5:1), and increases the mean 
greatest and least relative velocities of shooting-stars respectively to 44-43 
and 10-23 miles per second, which are to each other in the proportion of 
4:34:1. Supposing, then, that the whole vis viva of meteors is converted 
into heat and light, the heat developed on the surface of those which move 
to meet the earth directly is greater than that developed by meteors which 
directly overtake it, in the proportion of 19:1. It follows that the light 
and also the number of meteors in the former case visible to the naked eye 
will be proportionately greater than those in the latter; and should two 
meteorites of exactly equal masses penetrate the atmosphere, one of them 
moving from the direction of the apex of the earth’s way with the mean 
maximum velocity of meteors relatively to the earth, and the other from the 
opposite direction with the mean minimum velocity, the former meteorite 
may be totally volatilized, while the latter may reach the earth with a por- 
tion of its substance unconsumed, and may produce an aérolitic fall. In this 
manner Prof. Schiaparelli accounts for a fact which may at least be regarded 
as pretty well established t, that the greater number of aérolitic falls take 
place in the afternoon and evening hours of the day, although meteoric 
phenomena, generally, are then least vivid or abundant, because at that time, 
which corresponds to meteoric night, the anti-apew of the earth’s way is at its 
highest point above the visible horizon, and the meteoric showers which then 
make their appearance are for the most part moving in direct orbits, so as to 
overtake the earth with the minimum meteoric speed. 
Although no aérolites are precipitated from the meteor-currents of the 
« Perseids” and “ Leonids,” the elongations of whose radiant-points from the 
* Taking for the amount of the solar parallax its new value, 8'-95. The velocity both 
of the earth and of particular meteors may differ sensibly from the mean value. Thus, for 
Biela’s comet, whose periodic time of revolution is 6-7 years, the elliptic velocity at the 
point where it crosses the earth’s orbit is 1-14th part less than that of a parabolic orbit, or 
about 23:9 B.S. miles per second. The real velocity of the November meteors at the same _ 
point in their orbits is about 25-07 miles per second. 
+ See these Reports for 1860, p.117.—Table to Mr. Greg’s Catalogue of Aérolites. 
