Page:Popular Science Monthly Volume 7.djvu/642

624 active, capacious, and fertile mind. Few men have accomplished what Sir John LubbuckLubbock [sic] has in the departments of ethnology, zoölogy, 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 incomplete, the subject of it being yet in its infancy. That flowers and insects are intimately related has long been known, but the importance and extent of those relations 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 immemorial we have known that flowers are of great importance to insects, it is only of late that we have realized how important, indeed how necessary, insects are to flowers."

These ideas are illustrated and enforced by a series of careful and ingenious observations conducted by the author, "chiefly with the view of encouraging in his children 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.

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 respect 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 motions a family likeness.

Conversely, if we inquire what law of central force will cause two planets to obey the laws just quoted, we find that this central force must vary in intensity inversely as the square of the distance. Given Kepler'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 inquire what are the further laws, if any, which the members each fulfill, we find that there are resemblances, analogies, harmonies, but no exact laws which govern the masses, densities, rotation-periods, distances, etc. The law of Titius (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, likewise gives some striking coincidences, but our ignorance of the rotation-times of Mercury, 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 question, in pretty much 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 volume opens with 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