624 



THE POPULAR SCIENCE MONTHLY. 



active, capacious, and fertile mind. Few 

 men have accomplislied what Sir John Lub- 

 buck has in the departments of ethnology, 

 zoology, entomology, and several other 

 branches of science, and are, at the same 

 time, eminent and successful as he is in 

 financial and commercial enterprise. 



The present little volume will be read 

 with interest and profit ; although, as the 

 author modestly tells us, it is quite incom- 

 plete, the subject of it being yet in its in- 

 fancy. That flowers and insects are inti- 

 mately related has long been known, but 

 the importance and extent of those rela- 

 tions were scarcely suspected until recent 

 time. " It is our illustrious countryman, Mr. 

 Darwin," the author observes, " who first 

 brought into prominence the fact that the 

 importance of insects to flowers consisted 

 in their transferring the pollen, not merely 

 from the stamens to the pistil, but from 

 the stamens of one flower to the pistils of 

 another. . . , While, then, from time im- 

 memorial we have known that flowers are 

 of great importance to insects, it is only of 

 late that we have realized how important, in- 

 deed how necessary, insects are to flowers." 



These ideas are illustrated and enforced 

 by a series of careful and ingenious obser- 

 vations conducted by the author, " chiefly 

 with the view of encouraging in his chil- 

 dren that love of natural history from 

 which he has derived so much happiness." 



The work is illustrated by 130 figures, 

 has a glossary, and a copious index. 



Statement and Exposition of Certain 

 Harmonies of the Solar System. By 

 Stephen Alexander, LL. D., Professor 

 of Astronomy in the College of New 

 Jersey. Smithsonian Contributions to 

 Knowledge, No. 280. Washington, 

 1875. 



The laws of Kepler declare, with respect 

 to any one planet, that it moves in an ellipse 

 about the sun, which is at one focus of this 

 ellipse, and that the radius-vector of this 

 planet (the line joining it to the sun) sweeps 

 over equal areas in equal times : with re- 

 spect to any two planets, these laws declare 

 that the squares of their times of revolution 

 about the sun are proportional to the cubes 

 of their mean distances. This last law, as 

 Sir John Herschel has remarked, binds all 

 the planets together and gives to their mo- 

 tions a family likeness. 



Conversely, if we inquire what law of 

 central force will cause two planets to obey 

 the laws just (luoted, we find that this cen- 

 tral force must vary in intensity inversely 

 as the square of the distance. Given Kep- 

 ler's laws, we can arrive at this* law of force : 

 assuming this law of force, Kepler's laws 

 are a consequence. 



Now, if in the planetary system we in- 

 quire what are the further laws, if any, 

 which the members each fulfill, we find that 

 there are resemblances, analogies, harmo- 

 nies, but no exact laws W'hich govern the 

 masses, densities, rotation -periods, dis- 

 tances, etc. The law of Tit ins (or Bode's 

 law) gave numbers which approximated to 

 the mean distances of the major planets, 

 until Neptune was discovered, the mean 

 distance of which was strikingly different 

 from that which this rule would assign to 

 it. " Kirkwood's Analogy," which gives the 

 rotation-time of a planet when its time of 

 revolution about the sun is known, like- 

 wise gives some striking coincidences, but 

 our ignorance of the rotation-times of Mer- 

 cury, Venus, Uranus, and Neptune, does 

 not permit us to test it very closely. 



It has long been a fascinating branch 

 of inquiry to investigate the question of the 

 existence of such laws, and several inquirers 

 have worked assiduously at this quiestion, 

 in pretty m>ich the same way in which 

 Kepler worked at the discovery of his laws, 

 i. e., by pure trial of various hypotheses. 

 The volume before us contains the results 

 of such work, and we propose to present, in 

 brief, an analysis of these results. The vol- 

 ume opens witli a statement of Kepler's 

 laws, and with a table showing the values of 

 the masses, mean distances, and densities 

 which the author assumes as the bases of his 

 discussion. We notice here, as elsewhere in 

 the book, that such data are usually taken 

 not from the original sources, but at second 

 hand. With regard to the Masses as given 

 by the author, we note that the mass of 

 Neptune is not " the Poul-Kova deduction ; " 

 that the mass of Uranus should be credited 

 to Struve ; that Encke's mass of Mercury, 

 which is adopted, is not of equal value with 

 Le Verrier's, which has been published for 

 many years. 



In the second section the relations of 

 the mean distances are considered : if 

 of the distance of Neptune we take five- 



