31 
In that plane, it must be either an impulsive force acting once or 
it must be a constant force acting continually. ‘The only bodies in 
that plane are the comets and the sun, and if the force is a continu- 
ous force it must be from the comet or from the sun. It is almost 
inconceivable to suppose that the comet could have sent them off, 
either impulsively or continuously, in such a way as to give us the 
distance of 200,000,000 and 300,000,000 miles in the course of 
thirty years; it would require far more than any velocity that 
we Can give in our terrestrial experiments, and we have no reason 
to suppose that there is any such power of impulsion. Moreover, 
if the impulsion came from the comet, they would go in all direc- 
tions and their character, as being in a plane, would have been en- 
tirely lost. 
We are then thrown back on this one hypothesis, that the sun is 
the source of that force. In other words, we are led to extend the 
idea that I gave you in the beginning, and which is accepted by 
astronomers, that the material which goes off from the comet, after 
it leaves it, is subject to a force like that of attraction but differing 
in its intensity. In the case of the tail, it is a repulsive force. 
To satisfy these conditions of separation, part in one direction and 
part in the other, from the comet, we must have an attraction in 
the one case exceeding the attraction of gravitation and, in the 
other, an attraction less than the attraction of gravitation. In 
other words, these little bodies of hard matter that go off from the 
comet and follow very nearly in its train are acted on not in pro- 
portion to the force that steadily acts on the planets in their orbits. 
I see no escape, myself, from this conclusion. What it means, I 
must leave to you to decide. Our experiments make it very improba- 
ble that the attraction of matter differsin any way from proportion to 
the mass. It looks to me as though the more natural explanation 
is that, in some way, the materials which go off from the comet 
carry with them a load of electricity, or something of that kind, by 
which they have a permanent repulsion or permanent attraction 
sufficient to change the orbit altogether, not in kind, but in a 
steady change, throwing them into a new orbit with a new period, 
and thus scattering them. 
What that added force must be, we cannot very well tell, because 
it differs according to the place in the orbit where the disintegra- 
tion takes place. If that disintegration takes place near the sun, 
it is one thing; if it takes place near Jupiter, it is another. It 
