proceedings of the polytecnnic association. 349 



Harmonies of the Solar System. 



Prof. Kirkwood, of the Indiiuia State University, in a paper with this 

 title, published in the American Journal of Science and Art, has given his 

 latest deductions on the following subjects: 



I. ROTATION OF THE PLANETS. 



Under this head he presents views confirmatory of his celebrated "Analo- 

 gy," announced in 1849, that the square of the number of days in each 

 planet's year is as the cube of the diameter of its sphere of attraction, in 

 the nebular hypothesis. 



II. PLANETARY DISTANCES. 



After showing that Bode's law, so called, fails to represent even approx- 

 imately the relative distances of Mercury and Neptune, he repeats a state" 

 ment previously made by him, that the primary planets are arranged in 

 pairs, the members of which are nearly equal in diameter. Neptnne and 

 Uranus constitute the first pair; Saturn and Jupiter the second; the Aste- 

 roids and Mars the third; the Earth and Venus the fourth; finally Mercury 

 is without a known companion. In each of the three complete pairs, the 

 first, second and fourth, the densities of the members are very nearly as 

 their volumes. These facts seem to indicate a similarity in the original 

 constitution of the members of each pair, and an intimate mutual depend" 

 ence or connection in their primitive condition. It appeared not improbable 

 that in the first stages of their history, Neptune (ind Uranus constituted a 

 system of closely associated rings; Saturn and Jupiter another, &c., and 

 that the law of planetary distances might be found in the relative situations 

 of the centers of gyration of those binary rings. In short, his researches 

 on the subject led to the hypothesis that fhe differences of the radii of gyra- 

 tion of the jirimitive rngs form a geometrical series. 



After examining this hypothesis in relation to the planets, the author 

 proceeds to apply it to the secondary systems, the satellites of Saturn and 

 Jupiter. 



Relation of the Periodic Comets to the Solar System. 



After pointing out the relation of the mean distances of some of the com- 

 ets with the planets. Prof. Kii'kwood thus concludes: "May not the 

 exterior secondary rings, thrown off by the planets, have been at too great 

 a distance to form stable satellites ? and in such case would not detached 

 portions of the matter revolve around the sun in very eccentric orbits, the 

 degree of eccentricity depending on the direction of their motion at the 

 epochs of separation from the secondary system ? If so, the approximate 

 coincidence between the periods of planets and comets would follow as a 

 consequence." 



On the Distribution of the Dark Lines of the Spectrum. 



Prof. Henricks, of the Iowa State University, has studied the distribution 

 of these lines in elementary bodies, for the purpose of finding the laws 

 regulating them. Ilis investigations have led him to announce — 



I. That the mutual distances of different lines in each separate group are 

 the multiples of the smallest distance in such group. 



