NA JURE 



25 



THURSDAY, NOVEMBER 13, 



WORLD-LIFE 

 World-Life; or, Comparative Geology. By Alex. Winchell, 

 Professor of Geology in the University of Michigan. 

 Pp.642. (Chicago: Griggs, 1883.) 



AT the present day cyclopaedic knowledge has become 

 very rare, and a scientific man is generally like a 

 miner intent on his own special shaft, and too often care- 

 less or ignorant of the general plan of the whole mine of 

 science. The work of the collator and summariser is 

 thus continually rising in importance, and care, patience, 

 and judgment are now more requisite than ever before. 

 Although these scientific " consolidation acts " can hardly 

 fail to be open to criticism, yet every man of science must 

 receive them with gratitude, for they afford him a general 

 view of his science, and furnish him with a useful repertory 

 of reference. 



In this work Prof. Winchell's field is very wide, when 

 he undertakes to collate astronomy, cosmogony, and 

 geology, in the widest acceptation of these terms. So 

 many subjects does this book touch on that it will only be 

 possible within the limits of an article to give a general 

 view of its scope. The author's reading has been exten- 

 sive, and we are glad to observe that copious references 

 are provided. He expounds with care, although perhaps 

 sometimes too diffusely, the views of many writers, and 

 thus brings to a focus a great mass of literature, and his 

 own speculations are generally interesting, although not 

 always above criticism. 



As already indicated, this work is intended to give a 

 general survey of stellar and planetary systems, to note 

 the marks of evolutionary processes revealed by the tele- 

 scope, to discuss various cosmogonic theories, to examine 

 the probable life-histories of nebulae, suns, planets, and 

 satellites, and to consider the influences under which the 

 surfaces of planets are modelled and transformed. 



Modern cosmogony is properly a department of physics 

 and dynamics ; but when states of matter irreproducible 

 in the laboratory, and the mechanics of systems too com- 

 plex for rigorous mathematical treatment, are dealt with, 

 moderation in the general reasoning employed has not 

 always been duly observed. No one can doubt that 

 speculation is of the highest scientific importance, but it 

 is also equally certain that in work of this kind a descend- 

 ing scale may be formed, beginning with speculations 

 founded on rigorous mechanical principles and ending 

 with wild and lunatic fancies. Every writer on such 

 topics must, I suppose, sometimes question himself with 

 misgiving as to where in such a list his name would 

 stand. Mr. Winchell appears to treat all speculations 

 with judgment, although one is sometimes tempted to 

 think the exposition over-elaborate and the consideration 

 too patient 



The first part or book is entitled " World-Stuff," and 

 begins with a good account of meteors and meteoric dust. 

 The author thinks that, according to Mr. Aitken's theory 

 of the formation of fog, the highest clouds in our atmosphere 

 reveal the presence there of a very fine dust, probably of 

 cosmic origin. The sunset-glows of last winter appeared 

 Vol. xxxi. — No. 785 



to illuminate clouds at an unusual altitude : may not these 

 clouds have owed their existence to the very dust which 

 caused the glow ? 



The zodiacal light is then described, and is attributed 

 to swarms of meteorites circulating round the sun, and 

 the visibility of the light on both horizons simultaneously 

 is taken as showing that the orbits of some of them are 

 greater than that of the earth. The author also suggests 

 the probability that swarms of meteorites circulate about 

 the planets as satellites. 



Comets, whose association with meteorites is now 

 generally accepted, are described. Later (p. 77) the 

 author writes : — 



" The phenomena of the tail, especially in the vicinity 

 of aphelion, are such as would result if we could conceive 

 the nucleus of the comet surrounded by an aura extend- 

 ing on all sides as far as the remotest limits of the tail, 

 and could recognise the tail as merely a luminous shadow 

 cast by the nucleus in intercepting certain radiant energy 

 proceeding from the sun. . . . The tail would be, there- 

 fore, not a material form moving with the comet, but 

 something perpetually renewed, while the older and more 

 distant emanations disappear from visibility." 



That theory which divides the tails of comets into three 

 classes, according to the gas of which they are formed, is 

 not given. 1 



The nebula? are then passed in review, and are well 

 illustrated by drawings. They are classified as amor- 

 phous, spiral, spiro-annular, annular, and planetary, and 

 the class is taken as giving an indication of the stage of 

 evolution. 



In the case of a spiral nebula, such as that in Canes 

 Venatici (Fig. 8, op. oil.), it seems difficult to believe that 

 we view the whole. And we suggest that the great mass 

 of the gas is non-luminous, the luminosity being an evi- 

 dence of condensation along lines of low velocity, accord- 

 ing to a well-known hydrodynamical law. From this 

 point of view the visible nebula may be regarded as a 

 luminous diagram of its own stream-lines. 



In the second chapter the author enters on the genera- 

 tion of heat in nebular masses. The discussion appears 

 unsatisfactory, and as it is a matter of primary import- 

 ance, I propose to make some criticisms thereon. The 

 usage of mechanical and thermic terms is loose, so that it 

 is somewhat difficult to determine the author's meaning. 



The question is concerning the generation of heat 

 in a contracting nebular mass, and on p. 86, § 9, he 

 concludes : — 



" It is true, then, that contraction develops heat, and 

 that its development delays final refrigeration ; that is, 

 the progress toward final refrigeration is not as rapid as 

 the amount of radiated heat implies. But it is not true 

 that contraction (from cooling) can have developed the 

 whole amount of heat at any time existing in the mass, or 

 can even maintain a body at a constant temperature." 



From this conclusion I venture to dissent, and in order 

 to show my grounds I will give a paraphrase of the 

 author's argument, as far as I am able to grasp it. 



Let there be two similar planetary spheres with layers 

 of equal density similarly arranged, and let the linear 

 dimensions of the smaller (or say configuration /3) be 

 l-«th of those of the larger (or say configuration a) ; or, 



1 This was sketched by Prof. Ball in his late lecture at Montreal, but I 

 have unfortunately forgotten the originator's name 



