4.32 Notices respecting Nevo Books. 



system. Accordingly the system was extended by Kepler's discovery 

 of the proportions between the times of revolution of the planets and 

 their distances from the sun. Again, after Kepler had promulgated his 

 discoveries, Galileo discovered the satellites of Jupiter, and by ob- 

 servations on these, Kepler saw it ascertained that the law which he 

 had discovered to apply to the revolutions of the planets around the 

 sun, held good also when applied to the periods of circulation of the 

 satellites of Jupiter around that planet 3 " thus demonstrating it to 

 be something more than a mere empirical rule, and to depend on the 

 intimate nature of planetary motion itself."* But it was left for the 

 o-enius of Newton to complete, to a certain degree of generality, the 

 natural system of the planets which had been discovered by his pre- 

 decessors. It was shown by him, in the Principia, that all the celes- 

 tial motions which had down to his time been made known, were 

 consequences of one simple law of attraction. And the consequences 

 of this law, called that of gravitation, have been since pursued, through 

 all their intricacies, by Clairaut, D'Alembert, Euler, Lagrange, and 

 Laplace ; and they are still pursuing by the successors of those philo- 

 sophers, — by Ivory, Herschel, Airy, Lubbock, Poisson,and many others. 

 Now all this, we observe, is nothing but a series of investigations 

 having for their object the discovery of what, in Astronomy, exactly 

 answers to the natural system (now using that term in the highest 

 and most comprehensive sense) in Natural History ; and each con- 

 tributor, whether practical observer or mathematician, actually has 

 discovered some part of that system, — some portion of what was in- 

 cluded in the general natural system discovered by Copernicus, which 

 remained unknown until the time of the particular discoverer. It 

 will of course be remembered that we are comparing the progress 

 made in Astronomy with that of Natural History, here, merely for 

 the purpose of illustrating what we conceive to be the legitimate ob- 

 ject of the investigations of both, the discovery of the natural system; 

 and that the two sciences have been regarded as comparable, mutatis 

 viutandis only. And in the further comparison which follows, we beg 

 it to be observed that we are not in any manner intending to make 

 out a parallel, as to genius or scientific character, between the philo- 

 sophers we have named as the successive discoverers of the natural 

 system in astronomy with the naturalists we are about to name, as, 

 among others, the discoverers of the natural system in Zoology. We 

 presume not to offer any opinion on this point. 



One of the reasons which have induced us to enter upon this detail 

 of illustration, is the idea which has often been expressed, both orally 

 at various scientific meetings, and also in print, that the discovery of 

 the natural system is a thing which cannot or ought not to be aimed 

 at — that it is not a legitimate object of science. Our opinion being 

 diametrically opposite to this, we wish to show that what Mr. Mac- 

 leay and the naturalists of his school are endeavouring to accom- 

 plish for Natural History, exactly corresponds to what Copernicus, 

 Kepler, Newton, and Laplace have accomplished in part for Astro- 



• Herschel's Preliminary Discourse, p. 269. 



nomy. 



