D. Kirkwood on certain Harmonies of the Solar System. 17 
comets whose periods are included between those of Mars and 
Jupiter. Their motions are all direct; their orbits are less eccen- 
tric than those of other comets; and the mean of their inclina- 
tions is about the same as that of the asteroids. The perihelia 
5 are exterior to the earth’s orbit, and the nearest approac’ 
of Faye’s to the sun is several million miles beyond the orbit of 
ars. In fact, there is less difference between the eccentricity 
of the orbit of Faye’s comet and that of some of the asteroids, 
than between the latter and that of some of the old planets; so 
that this body may be regarded as a connecting link between 
planets and comets. These facts appear to indicate some con- 
nection in their origin with the zone of asteroids. 
Since the commencement of the present century, five comets 
have been discovered, which form, with Halley’s, an interesting 
and remarkable group. The first of these was detected by Pons, 
on the 20th of July, 1812; the second by Olbers, on the 6th of 
March, 1815; the third by DeVico, on the 28th of February, 
1846; the fourth by Brorsen, on the 20th of July, 1847; and 
the last by Westphal, on the 27th of June, 1852. The periods 
of these bodies are all nearly equal, ranging from 68 to 76 years; 
their eccentricities are not greatly different; and the motions of 
all, except that of Halley, are direct. The existence of these 
two cometary groups was noticed several years since both by 
Hind and Alexander. The latter supposes the cluster whose 
times of revolution are nearly equal to the period of Uranus, to 
have had a common origin. He infers from various facts that 
in the early part of the fourteenth century a large comet ap- 
roached very near to Mars, if indeed there was not an actual 
collision between the two bodies. This ancient comet he sup- 
poses was thus separated into fragments. That most, if not all, 
of this cometary group have had a common ry we reg 
as highly probable: we doubt, however, whether the true expla- 
nation of that origin has yet been proposed. 
Again: the comet discovered by Peters on the 26th of June, 
1846, has a period, according to the discoverer, of about 138 
ears; and Tuttle's comet (1858, I.) completes its revolution in 
13:6 years. The perihelion of each is exterior to the earth’s 
orbit, and their motions are direct. The periods of these bodies 
are a little greater than that of Jupiter. It may also be remarked 
that the comet which passed its perihelion on the 28th of No- 
vember, 1793, has, according to Burckhardt, a period of 12 years. 
The period of the great comet of 1843 is probably nearly the 
same with that of Neptune. Other coincidences might be 
pointed out, but the periods in most cases are too doubtful to be 
‘Yelied upon. Those which we have adduced seem to point to 
an approximate coincidence between the mean distances of the 
planets and those of the periodic comets. 
Am, Jour. Sct.—Sreconp Serres, Vou. XX XVIII, No. 112.—Junrr, 1864. 
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