358 
POPULAR SCIENCE REVIEW. 
sort that Jupiter exerts his most powerful retardative influence, 
must have moved for some time previously in such a way that 
Jupiter exerted nearly his most powerful accelerative influence.* 
It may he readily shown to he impossible for Jupiter to with- 
draw much more velocity than he had already communicated ; 
and similar remarks apply, of course, to Saturn, Uranus, and 
Neptune. 
The application of these considerations to Schiaparelli’s theory 
is easily perceived. In order that a particle attracted from outer 
space may be compelled to travel in a closed orbit around the 
sun, its velocity must be diminished. And this can very readily 
happen. But for the particle to travel in an orbit of a 
particular extent or mean distance, its velocity where it crosses 
the distance of the disturbing planet must be diminished by a, 
certain amount ; and in dealing with Schiaparelli’s theory, it is 
a cardinal consideration whether the observed orbits of periodic 
comets are such that we can admit the possibility of their 
resulting from any diminution of velocity which the disturbing- 
planet could have produced. Taking, for instance, the November 
meteors, which pass near the orbits of Uranus and the earth, 
and do not approach any other orbit near enough for any such 
effects upon the orbital motions of these bodies as we are now 
dealing with.f We may dismiss the earth from consideration 
at once, because our planet is far too small to modify the 
motions of bodies rushing past her with the velocity, nearly 
26 miles per second, which the sun communicates to bodies 
approaching him from interstellar space, by the time they reach 
the earth’s distance from him. Uranus then alone remains. 
Now the present velocity of the November meteors when crossing- 
the orbit of Uranus amounts to about 1J miles per second. 
The velocity of a particle approaching the sun from interstellar 
space would be nearly 6 miles per second when at the distance 
of Uranus. It may be seriously questioned whether, under any 
* It is manifest that a particle in approaching from without must he, in 
the first instance, accelerated by any planet to which it draws near, no- 
matter what the direction may be in which the particle arrives. It may 
begin to be retarded, however, before it has reached the distance from the 
sun at which the disturbing planet is travelling. In any discussion of the 
change of path as to position, w’e should need to inquire very carefully into 
the manner of approach ; but in the above discussion we are only inquiring^ 
into the change of velocity. 
t Both Jupiter and Saturn can perturb the November meteors, and thus 
modify the shape and position of the meteoric orbits j but such changes, 
though by no means inappreciable, are utterly insignificant compared with 
those required to change the motion of a body approaching the sun from 
interstellar space into motion in an orbit like that of the November 
meteors. 
