30 
would form across the sky a single line instead of a broad, expand- 
ed mass of light such as we see. From the comet, however, there 
are driven off also, or there are separated other things entirely dis- 
tinct from the tail, small bodies, which are not thus driven away, 
which are not visible, but follow along closely in the path of the 
comet, and whenever the occasion comes, that is when we go through 
a group of them, those give us our shooting stars. 
The Biela comet, in the period about 1840, passed near to 
Jupiter. At that time it was turned pretty sharply out of its orbit, 
the inclination of the orbit being turned several degrees, and the 
node being carried forward also several degrees, represented by 
several days in the time at which we crossed the path of the comet. 
After 1840 the bodies which formed the meteors that were met in 
1872 and in 1885 were separated from one or other parts of the 
Biela comet. I say after 1840, because if they had been separated 
earlier they would have given us a different radiant in the skies, 
the one given by the Biela meteors of 1838. The radiant was 
changed, the node was changed, all to correspond to the new orbit, 
and these bodies could not have been turned in that way had they 
been before scattered, because the force that acted on them, the attrac- 
tion of Jupiter, would have scattered the group instead of giving us 
that single compact group through which we passed in 1872 and 1885 
in the course of four or five hours, and the bulk of them even in two 
hours. 
In 1872, the comet was something like 200,000,000 miles away 
from the bodies that we met as we passed through them on the 27th 
of November, giving us a brilliant shower. ‘Thirteen years later we 
passed through the group again, and then the comet was something 
like 300,000,000 miles ahead of the group. So that some of the 
particles, leaving the comet between 1840 and 1870, had gained 
and others between 1840 and 1885 had fallen behind. 
What should separate those particles ? What are the forces which 
carried off those particles so many miles—200,000,000 miles on the 
one hand and 300,000,000 miles on the other, in round numbers ? 
The force that acts on them must be a force acting in one plane, 
that is, the plane of the orbit of the comet. Any force acting in 
other planes would have scattered the group and we would not have 
met them as a single definite group at the times named; but if it 
acts in the plane, only scattering them on the plane, they would be 
together as we saw them. 
