LITERARY NOTICES. 



849 



vation than even the prominences ever reach, 

 and seems to be not wholly gaseous, but to 

 contain, besides the hydrogen and the mys- 

 terious ' corouium,' dust and fog of some 

 sort, perhaps meteoric." 



While the part of the book devoted to 

 the sun is so excellent, it must not be sup- 

 posed that the other divisions of the subject 

 have not received adequate attention. In 

 fact, one of the strong points of the work is 

 that it is well balanced, and the student gets 

 as complete a view of the science as is pos- 

 sible within the limited space of a school 

 text book. The author, in setting forth with 

 uncommon clearness the elementary mathe- 

 matics of his subject, has not ignored what 

 may be called its philosophical aspects. He 

 has, for example, given an account of the 

 nebular hypothesis which, notwithstanding 

 its brevity, can not fail to be of much use in 

 dissipating the fog that hangs over this 

 ■whole subject in the minds of those who 

 have little knowledge of astronomy beyond 

 what has been vouchsafed to them in the 

 ordinary college curriculum. We should 

 have been pleased to see from Prof. Young's 

 pen an elementary account of George Dar- 

 win's remarkable theory of " tidal evolution," 

 in place of the references that are given to 

 other popular explanations of that subject. 



Recent discoveries have carried us so far 

 into the depths of space that there is nothing 

 within the circuit of astronomical knowl- 

 edge and investigation which appeals more 

 strongly to inquiring minds than the rela- 

 tions of the solar system to the universe 

 without. Such achievements in observation 

 as those of the Lick telescope, and the re- 

 cent surprising advances in astronomical 

 photography, promise us much light upon 

 the old problem of the structure of the 

 heavens. Prof. Young's remarks in the 

 present work on the distribution and mo- 

 tions of the stars, though brief, are fruitful 

 in suggestion. We quote the following pas- 

 sage as a particularly interesting generali- 

 zation : " In the solar system the central 

 power is supreme, and perturbations or de- 

 viations from the path which the centnal 

 power prescribes are small and transient. 

 In the stellar system, on the other hand, the 

 central force, if it exists at all (as an attrac- 

 tion toward the center of gravity of the 

 whole mass of stars), is trifling. Perturba- 

 VOL. xxxiv. — 54 



tion prevails over regularity, and ' individu- 

 al.ism ' is the method of the greater system 

 of the stars, as solar despotism is that of 

 the smaller system of the planets." 



This remark, which is fully justified by 

 all we now know of stellar motion, presents 

 a very different picture of the universe from 

 that which has sometimes been drawn for 

 the edification of admiring congregations, of 

 planets circhng around suns, and suns around 

 other suns, and these systems around grand- 

 er systems still, and finally the whole uni- 

 verse revolving with a stupendous orbital 

 sweep around the great center of all, the 

 throne of the Creator himself ! It appears 

 that things don't revolve that way. 



There are many good features in the 

 book that we should like to point out if 

 space permitted. It may be remarked, by 

 the way, that a fine example of the author's 

 desire to convey practically useful informa- 

 tion is the italicized sentence on page 35 : 

 " Never turn the hands of a chronometer 

 backward.'''' 



It goes without saying that the more 

 mathematical parts of Prof. Young's work 

 are highly excellent, succinct, and clear. 

 Such subjects as central forces, the tides, 

 parallax, the equation of time, and perturba- 

 tions are treated in such a way as to give 

 the student a sure insight into the nature of 

 the problems involved. 



The illustrations accompanying the text 

 are good, many being original, and some ex- 

 cellent ones borrowed from the author's 

 book on " The Sun " (published by Apple- 

 tons), and from other sources. Some useful 

 tables of elements and constants, based upon 

 the most recent information, close a book 

 which, it is not too much to say, will be 

 scarcely less welcome to the general reader 

 than to the students for whose instruction it 

 is intended. 



Force and Energy : A Theory of Dynamics. 



By Grant Allen. London and New 



York : Longmans, Green & Co. Pp. 16L 



Price, ,f 2.25. 



Mr. Allen's theory does not aim to revo- 

 lutionize the generally accepted ideas con- 

 cerning force, but is rather an attempt to 

 classify the known forms of force, and sys- 

 tematize their relations. Under the general 

 term power he includes forces and energies, 

 distinguishing them by their effects. Thus, 



