

ASTRONOMY AND METEOROLOGY. 



KIRKWOOD'S ANALOGY. 



AT the recent meeting of the American Association, an announce- 

 ment was made, which, it' it is found to be correct, will be regarded as 

 relating to one of the most important discoveries which have been 

 made in astronomy for years. It is no less than a new law of the 

 solar system, closely resembling those of Kepler, which form the 

 groundwork of many of the problems of Astronomy. Mr. S. C. Walker 

 read to the Association a letter from Mr. Daniel Kirkwood, of Potts- 

 ville, Pa., the discoverer of this new law, from which we make some 

 extracts, omitting all that refers to the higher branches of mathe- 

 matics. 



" While we have in the law of Kepler a bond of mutual relation- 

 ship between the planets, as regards their revolutions around the sun, 

 it is remarkable that no law regulating their rotations on their axes 

 has ever been discovered. For several years I have had little doubt 

 of the existence of such a law in nature, and have been engaged, as 

 circumstances w r ould permit, in attempting its development. I have at 

 length arrived at results, which, if they do not justify me in announ- 

 cing the solution of this important and interesting problem, must at 

 least be regarded as astonishing coincidences." 



After stating some equations, he gives the following tables as the 

 data on which he has proceeded. 



Planet's 

 name. 



Mercury, 



Venus, 



Earth, 



Mars, 



Jupiter, 



Saturn, 



Uranus, 



Mean dist. from 

 the Sun in miles. 



36,814,000 



68,787,000 



95,103,000 



144,908,000 



494,797,000 



907,162,000 



1,824,290,000 



Mass. 



277,000 



2,463,836 



2,817,409 



392,735 



953,570,222 



284,738,000 



35,186,000 



Square root No. of rotations 

 of mass, in one sid. period. 



87.63 

 230.90 

 366.25 

 669.60 

 10,471.00 

 24,620.00 



526.3 



1569.6 



1678.5 



626.7 



30879.8 



16874.1 



5931.5 



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

 the number of a primary planeCs days in its year, is as the cube of the 

 diameter of its sphere of attraction in the nebular hypothesis" 



