LITERARY NOTICES. 



373 



measure due to the enlightened liberality 

 of the trustees of the Johns Hopkins Uni- 

 versity, who have prompted the undertak- 

 ing, and guaranteed a considerable portion 

 of the pecuniary risk attendant upon it." 



It is needless to say that this periodical 

 is in no sense popular, and is wholly unin- 

 telligible to non-mathematical readers. But 

 it deserves to be sustained in the interest 

 of higher American scholarship, and public- 

 spirited men, who can make it of no use to 

 themselves, may nevertheless promote a 

 good work by subscribing for it, and pre- 

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Tropical Nature, and other Essays. By 

 Alfred R Wallace. New York : Mac- 

 millan & Co. Pp. 356. Price, $3.50. 



Mr. Wallace's new volume consists of 

 some eight essays, of which the first four 

 only can be strictly considered as coming 

 within the scope of his principal title. Two 

 of the chapters have already appeared in 

 MacmillarCs Magazine ; one has been pub- 

 lished in the Fortnightly Review, and one 

 was originally delivered as a presidential 

 address to the Biological Section of the 

 British Association in 1876. Hence the 

 whole work comprises a slightly hetero- 

 geneous mixture, and the first three essays 

 have rather the appearance of an after- 

 thought, inserted for the purpose of giving 

 a consistent raison d'etre to the publication, 

 than that of a complete and consecutive 

 treatise. But, of course, Mr. Wallace can 

 never be otherwise than ingenious and in- 

 teresting, nor does the present volume form 

 any exception to the general excellence of 

 his compositions. 



The author sets out by stating that, 

 while the luxuriance and beauty of tropical 

 Nature are a well-worn theme, which has 

 often suffered from the undue exaggeration 

 of its exponents, no attempt has yet been 

 made to give a broad sketch of those phe- 

 nomena which are essentially tropical, and 

 which mark the chief differences between 

 equatorial aud temperate climates. This 

 desideratum he seeks to supply, from the 

 exceptional experience of a long residence 

 in the hottest regions of the Eastern and 

 the Western Hemisphere alike. In pursu- 

 ance of the design thus laid down, the first 



essay treats of " The Climate and Physical 

 Aspects of the Equatorial Zone," both as 

 regards their actual phenomena and the 

 causes which lead to their production. 

 Though possessing, of course, little absolute 

 novelty, the facts are well arranged, and so 

 displayed or illustrated as to bring the 

 salient points of tropical meteorology in a 

 very vivid manner before the untraveled 

 student. The second essay, on " Equatorial 

 Vegetation," contains an admirable sketch 

 of the tropical flora, viewed in its ensemble, 

 besides a vigorous exposition of the com- 

 mon but fallacious belief that large and 

 brilliant flowers are exceptionally frequent 

 in hot climates. Mr. Wallace succeeds in 

 giving a clear and sufficient notion of the 

 richness and profusion of vegetable growth 

 without rousing any suspicion of that false 

 theatrical glamour which ordinary writers 

 have cast around the subject. The third 

 essay deals with " Animal Life in the Tropi- 

 cal Forests," dwelling especially upon the 

 Lepidoptera and Hymcnoptera among in- 

 sects ; the parrots, pigeons, and picarias 

 among birds ; and the monkeys and bats 

 among mammalia all of which form the 

 peculiarly equatorial types of their several 

 classes. 



But it is with the fourth essay, on 

 " Humming-Birds," reprinted from the 

 Fortnightly Review, that the real interest of 

 the work begins. Mr. Wallace gives a 

 short sketch of the structure and habits of 

 these birds, and then takes the species 

 which inhabit the island of Juan Fernan- 

 dez as illustrations of the action of variation 

 and natural selection. In a bold and suc- 

 cessful a priori reconstruction of their his- 

 tory, amply justified by the incidental veri- 

 fications which crop out during the course 

 of the argument, he traces their origin, 

 with great probability, to two separate acci- 

 dental migrations, under stress of weather, 

 from the opposite coast of Chili. At the 

 same time he shows the probable causes of 

 the resulting variations, and starts a theory 

 of organic coloration, which is more fully 

 treated in the two succeeding essays. He 

 then points out the strong structural resem- 

 blances between swifts and humming-birds, 

 while demolishing the supposed connection 

 between the latter and their Eastern repre- 

 sentatives, the sun-birds a connection based 

 entirely upon adaptive and functional pe- 



