May 23, 1878] 



nature:'-!^ 



9' 



though occasionally successful for a moment, is the most 

 wasteful and destructive of all methods of sharpening 

 the teeth. 



What we have at some length discussed is the most 

 prominent feature of the present work, but by no means 

 its only distinctive one. No writer, who has any claim 

 upon his readers at all, can treat even the most hackneyed 

 subject without giving a new and useful turn to many a 

 Ipng-known truth. Many of Prof. Clifford's proofs are 

 exceedingly neat, and several useful novelties {e.g. 

 Three-bar Motion) are introduced. We have to com- 

 plain, however, of a great deal of unnecessary new and 

 very strange nomenclature ; — for a large part of which 

 the author is not responsible, his error (for such we cannot 

 help considering it) consisting in giving this stuff a place 

 of honour in his book. One does not require to be very 

 violently conservative to feel dismayed at an apparently 

 endless array of such new-fangled terms as Pedals, Rotors, 

 Cylindroids, Centrodes, Kites, Whirls, and Squirts ! Yet 

 these are but a few gleaned at random from the book. 

 Something, it seems, must be hard in a text-book — 

 simplify the Mathematic, and the Anglic {i.e. the English) 

 immediately becomes perplexing. P. G. Tait 



PHYSICS OF VOLCANOES 

 Beiirc.g zur Fysik der Erupiionen und der Eruptiv- 

 Gesteine. Von Dr. Ed. Reyer, Decent an der Uni- 

 versitat in Wien. (Vienna : Alfred Holder, 1877.) 



DR. Reyer, of Vienna, has already made his mark in 

 geological literature by the admirable work entitled 

 " Die Euganeen : Bau und Geschichte eines Vulcans," 

 in which he has given a very clear and instructive inter- 

 pretation of the phenomena presented by that grand 

 tertiary volcano of Northern Italy, of which the internal 

 structure has been so well displayed to the geologist 

 through the agency of denuding forces. Those who are 

 acquainted with the merits of the first published work of 

 Dr. Reyer will eagerly take up the volume which has now 

 made its appearance, the title of which stands at the 

 head of the present notice ; nor will their anticipations 

 that a difficult question will meet with masterly and 

 original treatment at the hands of its author be disap- 

 pointed. 



A starting-point for a series of discussions of the phe- 

 nomena of volcanic action and the causes to which these 

 are due is found by Dr. Reyer in the demonstrated 

 capacity of various substances in a state of igneous fusion 

 for absorbing certain gases. If the suggestion that in 

 this peculiar property of bodies in a state of fluidity under 

 the action of heat we find a key to many of the most 

 remarkable phenomena of volcanic eruptions be not alto- 

 gether new, it must at least be admitted that it has never 

 before received such ample discussion and illustration as 

 it now undergoes in the hands of Dr. Reyer, and even 

 still less has hitherto been done in applying the explana- 

 tion in question to these numerous minor and concomi- 

 tant phenomena which precede, accompany, and follow 

 volcanic outbursts. 



In the first part of the work before us, the author, 

 after citing the interesting observations of Gay Lussac, 

 Foumet, Thenard, Reaumur, and other chemists, in proof 

 of the property of absorption as displayed by substances 



in a state of igneous fusion, goes on to show that many 

 of the striking appearances exhibited during volcanic 

 eruptions clearly point to the conclusion that a highly- 

 heated magma within the earth's crust has, through infil- 

 tration, become charged with liquid and gaseous materials. 

 He then proceeds in the second part of the volume to show 

 how many of the phenomena of volcanoes — such as the 

 succession of events in the history of their formation and 

 in that of each individual eruption, the peculiarities of the 

 internal structure of volcanoes and of the masses of lava 

 extruded from their vents, and the nature of the gaseous 

 exhalations which accompany the outbursts during their 

 several stages — receive a simple explanation from this 

 remarkable property exhibited by substances in a state of 

 fusion. 



Apart, however, from the value of its more speculative 

 portions, Dr. Reyer's work will be welcomed by geologists 

 as bringing together in a connected form all the most 

 important of the recent observations which have been 

 made upon the nature and products of volcanic activity. 

 It is in this respect that the third part of the work before 

 us, that which deals with the peculiarities of volcanic 

 rocks, appears to us to be especially worthy of attention. 

 The author not only admits that the principle which haa 

 been so long followed by German petrographers, of basing 

 the classification of igneous rocks on their geological age, 

 is altogether untenable, but he goes farther and strongly 

 denounces the mischievous tendencies of this method in 

 obscuring some of the most striking inferences to be 

 derived from the exact study of such rocks. Strongly 

 insisting on the fact that portions of the same magma 

 may, under different physical conditions, assume a granitic,, 

 a porphyritic, or a vitreous structure. Dr. Reyer shows 

 clearly how the various igneous intrusions found associated 

 with sedimentary deposits were in all probability origin- 

 ally connected with centres of volcanic activity ; and he- 

 also shows the grounds for the inference that masses of 

 granitic structure are being formed at the present day 

 by the slow consolidation under pressure of portions oJt . 

 the magma below the existing volcanic vents. 



Of the urgent necessity for reforms in our petrographical 

 nomenclature, the author of this work, holding the views - 

 he does, clearly perceives the necessity ; and his sugges- 

 tions upon the subject deserve, as they doubtless will 

 receive, the careful attention of geologists. Some of the 

 interesting relations between the structure and composi- 

 tion of rocks are, we may remark in passing, very well 

 illustrated by the series of ingenious diagrams which * 

 accompany this volume. J. W. J. 



OUR BOOK SHELF 



Travels ht the Footsteps of Brtice in Algeria and Tunis j- 

 Illustrated by Facsimiles of his Original Drawings. 

 By Lieut.-Col. R. L. Playfair, H.B.M. Consul-General 

 in Algeria. (London : C. Kegan Paul and Co., 

 1877-) 

 The northern regions of Africa that border on the 

 Mediterranean Sea would form a deeply interesting 

 study for the historian. Perhaps no other portion 

 of the world's surface has passed through more marked 

 phases of civilisation, yet all of these have passed 

 away and left but small trace behind them. Placed be- 

 tween a wondrously teeming offshoot of the Broad Atlantic 



