166 



Kirkwood's Analogy in the Periods of 



From these data he deduces the following law : — " The square of 

 the number of a primary planet^s days in its year, is as the cube of 

 the diameter of its sphere of attraction in the nebular hypothesis.'' 



" The points of equal attraction between the planets severally 

 (when in conjunction), are situated as follows : — 



Between Mercury and Venus, 

 " Venus and the Earth, 

 " Earth and Mars, 

 " Jupiter and Saturn, 

 " Saturn and Uranus, 



Miles from the 

 former. 



8,029,600 



12,716,600 



36,264,600 



266,655,000 



678,590,000 



Miles from the 

 latter. 



23,943,400 



13,599,400 



13,540,400 



145,710,000 



238,538,000 



" It will be seen from the above^ that the diameter of the earth*s 

 sphere of attraction is 49,864,000 miles. Hence the diameters of 

 the respective spheres of attraction of the other planets, according to 

 my emperical law, will be found to be as follows : — 



Mercury, 



Venus, 

 Mars, 

 Jupiter, 

 Saturn, 



Diameter of sphere 

 of Attraction. 



19,238,000 



36,660,000 



74,560,000 



466,200,000 



824,300,000 



" The volumes of the sphere of attraction of Venus, Mars, and 

 Saturn in this table, correspond with those obtained from the pre- 

 ceding one; that of Mars extending 61,000,000 miles beyond his 

 orbit, or to the distance of 206,000,000 miles from the sun. This 

 is about 2,000,000 or 3,000,000 miles less than the mean distance 

 of Flora, the nearest discovered asteroid. That of Mercury extends 

 about 11,000,000 miles within the orbit; consequently, if there be 

 an undiscovered planet interior to Mercury, its distance from the 

 Sun, according to my hypothesis, must be less than 26.000,000 

 miles. Jupiter's sphere of attraction extends only about 200.000,000 

 of miles within his orbit, and leaving 89,000,000 miles for the 

 asteroids. It is only in the most distant portion of this space, where 

 small bodies would be likely to be detected, that none have yet been 

 discovered." 



