Rotation of the Primary Planets. 397 
Diam. of Sphere of Attr. Log. 
Mercury, . ? . 19,238,000 1-283704 
Venus, , ‘ ‘ 36,660,000 1564218 
Mars, . ; ‘ . 74,560,000 1:872479 
Jupiter, . ‘ , 466,200,000 2°668594 
Saturn, ' . 824,300,000 2°916127 
Remarks.—The volumes of the sphere of attraction of Venus, 
Mars, and Saturn, in this table, correspond with those obtained 
from Table II; that of Mars extending sixty-one million miles 
beyond his orbit, or to the distance of two hundred and six mil- 
lion miles from the sun. This is about two or three million miles 
less than the mean distance of Flora, the nearest discovered aste- 
roid. ‘That of Mercury extends about eleven million miles with- 
in the orbit; consequently, if there be an undiscovered planet in- 
terior to Mercury, its distance from the sun, according to my hy- 
pothesis, must be less than twenty-six million miles. Jupiter’s 
sphere of attraction extends only about two hundred million miles 
_ Within its orbit, leaving eighty-nine million miles for the asteroids. 
It is only in the most distant portion of this space, where small 
bodies would be less likely to be detected, that none have yet 
been discovered.* a" 
The foregoing is submitted to your inspection with much diffi- 
dence. An author, you know, can hardly be expected to form a 
a8 estimate of his own performance. When it is considered, 
wever, that my formula involves the distances, masses annual 
revolutions, and axial rotations, of all the primary planets in the 
system, I must confess, I find it difficult to resist the conclusion 
that the law is founded in nature. 
Very respectfully, your obedient servant, 
Danie Kirxwoop. 
We annex the following Letter, dated Pottsville, January 23, 
1850, from Mr. Kirkwood containing a brief history of his very 
Important discovery.—Ebs. 
Wt emark that one planet between Mars and Jupiter, with a 
Saneniand 5 sare oe sa about double of the former, would perfectly satis- 
fy the conditions of my theory. 
