1885.] Comet Systems. jgg 
to the space from whence it came. Hence in this case the 
orbit would be hyperbolic. A true parabola, however, re- 
quires such a nice adjustment that the least disturbance 
may transform it into an ellipse or hyperbola. 
Now comets with hyperbolic orbits acknowledge neither 
permanent mle nor governance. They come down into our 
system with such a rush that the swiftly moving planets 
seem reduced to rest in comparison; but after their peri- 
helion swoop they, in all cases, return to wander alone in 
space. Nevertheless it seems certain that comets are cer- 
tainly captives fiom the realms of space. One theory, and 
°. ne . onl y> regards comets as originating within the 
limits of the Solar System, is worthy of discussion, — the 
theoiy, namely, that cornets are disgorged from the planetary 
volcanoes or erupted from the Sun. Yet even this when 
examined is found to be defective. For is it probable that 
Saturn or Jupiter could belch forth matter with a velocity 
sufficient to carry it in a retrograde direction round the Sun, 
after the respective manner of the comets of Temple (1866) 
and Halley ? Surely not, since a velocity of projection of 
35 miles a second would only just enable a comet to pass 
clear of Jupiter’s attraction ! Could the Sun, either, drive 
matter, such as comets are apparently made of, through his 
dense atmospheric envelope with a velocity sufficient to carry 
them for ever beyond his rule ? In all possibility, when the 
depth and density of his elastic covering is taken into 
account, a velocity of 500 miles per second* would be insuf- 
ficient ! It is safer, then, to conclude that comets are 
entirely of extra-solar and extra-stellar origin. 
But it may occur to the reader that we have just endea- 
voured to show that a comet advancing with a pre-received 
velocity into the Sun’s domain could not remain as a per- 
manent member of the Sun’s family, unless by accident. 
This is just ; and previous writers, who have held that 
comets are originally from without, have, in reply to this 
very question, formulated very elaborate hypotheses about 
comets being held in bondage by the Sun in consequence of 
“ the disarrangement of their orbits by planetary influence,” 
and so forth. Now it seems to me that this last supposition 
also is too imaginary to stand its ground for a single instant. 
We must, I fancy, go back into the Ages, to a time when 
the Sun ranked as a nebulous star, if we wish to arrive at 
the epoch when the Sun’s cortege of comets were captured 
and reduced to a fair amount of obedience. 
* This velocity of proje&ion has been observed ; it does not follow how- 
ever, that the erupted matter was necessarily a comet. 
