Boiation of the Primary Planets, 169 



• 

 diameter of the sphere of attraction, a fundamental element in this 

 analogy, now for the 6rst time gave an appearance of reality to 

 Laplace's nebular hypothesis which it never had before. The posi- 

 tive testimony in its favour would now outweigh the former negative 

 evidence in the case, however strong it may have been. It follows 

 at least from Kirkwood's analogy, that the planets were dependent 

 upon each other, and therefore connected in their origin, whatever 

 may have been the form of the connection, whether that of the ne- 

 bular hypothesis, or some other not yet imagined. 



At a later period of the meeting, M. B. A. Gould junior, stated 

 that he had gone through the necessary calculations, using different 

 quantities, and had come to the same conclusions as Mr Walker. 

 He expressed his opinion, tliat at some future day the world will 

 *' speak of Kepler and Kirkwood as the discoverers of great planetary 

 laws." 



The members generally expressed the opinion, that Laplace's 

 nebular hypothesis, from its furnishing one of the elements of Kirk- 

 wood's law, may now be regarded as an established fact m the past 

 history of the solar system. — American Annual of Scientific Dis- 

 covery , p. 335. 



Note. — Such, at least, is rather a representation of American 

 opinions than of our own. We are inclined to compare it more with 

 Bode's law than with Kepler's. The former is a mere arithmetical 

 accident, applying indifferently well to a portion only of the planets, 

 and having nothing of reason to advance for its establishment. The 

 latter are essential parts of mechanics and gravitation, and precisely 

 and perfectly, and necessarily true, not only in every part of the 

 solar system, but through the whole universe. 



The fact of axial rotations being the groundwork of Kirkwood's 

 analogy seems fatal to it, for gravitation takes no more account of 

 the time of rotation of a planet than it does of specific gravity ; all 

 calculations of the movement of the body in space are equally inde- 

 pendent of the one and the other. 



Under these circumstances, the degree of accuracy with which it 

 may be found to apply is the only saving clause. Messrs Walker 

 and Gould investigating the subject independently, and with better 

 constants of mass and distance than Kirkwood had been able to pro- 

 cure, declare that it appears perfectly I We are sorry that the late 

 hour at which we have received this paper has prevented us either 

 from giving it in full, or from testing the theory rigidly. 



It will be observed that, according to Kirkwood's theory, in order 

 to compute the time of axial rotations of any planet, it is necessary 

 to have its mass and mean distance, together with the same quanti- 

 ties tor the planets on either side of it. Now, these quantities are 

 only obtainable for Venus, the Earth, Saturn, and Uranus (a planet 

 being lost between Mars and Jupiter) ; and the rotation of Uranus 



