1872.] Meteoric Astronomy. I51 
the theory that the comet which produced it was in the first 
instance expelled from Uranus. We need not conclude, if 
we accept such a view, that the period named by Leverrier for 
the introduction of the comet into the solar system (A.D. 126) 
was necessarily the epoch of the expulsion of the comet by 
Uranus. The true epoch of this event may have been far 
more remote.* 
This, at any rate, is certain, that if the comets belonging 
to our system have been introduced, as is commonly sup- 
posed, by planetary perturbing influences, then the actual 
number of arriving comets must have indefinitely exceeded 
the number captured in this way. For an arriving planet 
has a million chances of escaping for one of being cap- 
tured,—so closely must it approach to one of the major 
planets if its motion is to be sufficiently controlled to cause 
it to become a permanent member of the solar system, with 
a perihelion near enough for the inhabitants of earth to 
recognise the comet, and with an aphelion not greatly 
beyond the orbit of the disturbing planet. 
But be this as it may, the connection between meteors 
and comets remains an established fact, the existence 
of many comets in the solar system is.a reality, and the fact 
that the earth encounters more than a hundred meteor 
systems cannot be disputed. 
Now, if we consider what proportion of interplanetary space 
the earth really traverses, we shall begin to recognise one of 
the most surprising of the conclusions which are deducible 
from these demonstrated facts. If the earth were really, as 
she is sometimes pictured, a globe so large that in an ordinary 
picture of her orbit around the sun she would be presented, 
to scale, as a considerable sphere, there would be nothing 
very remarkable in the circumstance that on her course 
round the sun she should come into contact with many 
meteor systems. But when we are reminded that on so 
large a scale that the earth’s orbit would be represented 
by a circle ten feet in diameter, the earth herself would 
be but about the rgoth of an inch in diameter, so that the 
path her globe actually traverses would be represented by a 
circle 10 feet in diameter, and marked in with about as 
stout a stroke as the down strokes of the letters in this 
page, we see at once how minute a portion of sun-sur- 
rounding space this ring-orbit really occupies. Remembering 
* It is also possible to account for the present position of the November 
meteor system by supposing that the encounter took place during that remote 
period when Uranus (according to the nebular theory) occupied a much larger 
region of space than at present. 
