5<H 



NA TURE 



[February 19, 1903 



-electric currents in the hands of Ampere and his 

 successors ; no mention need be made of the aether 

 until electric radiation begins to play a sensible part ) 

 either in the establishment of the field or in the 



■draining off of its energy, or until motion of the electric 

 charges is contemplated. In the latter case, it would 

 appear that we have either to take the aether to be at rest 

 or to say with our author that it behaves as if it were so. 

 The analogy has here been drawn (which Mr. Mac- 

 donald doubtless would not allow) between the analysis 

 of the interactions of electric currents in an aether which 

 is intangible and that of vortical smoke-rings in an 

 atmosphere which is invisible. In each case, one would 

 try to avoid assuming unnecessary properties of the 

 medium. And it is only fair to admit that the properties 

 of electric currents have actually been discovered in this 

 way, while without discussing the fluid we should hardly 



■ nave made much progress with the more fugitive 

 vortexes. 



The process of arriving at wider and wider points of 

 view by successive stages of generalisation from an initial 

 hypothesis is a familiar and fruitful one in theoretical 

 physics ; though in these latter times the logical and 

 philosophical merits of the converse process of discarding 

 from our knowledge all colorable images or analogies, in 

 favour of bare mathematical expression of the relations 

 •of the unknown quantities which are symbols for entities 

 on which we do not wish to dogmatise at all — of 

 which we, in fact, know intrinsically no more than we do 

 about the most common objects around us — has also been 

 amply enforced. Yet in successful instances of this latter 

 procedure, the retort seems open that the hypothesis 

 or analogy has not been dispensed with until it has 

 effectively disclosed of what type the said relations were I 

 to be. It very likely arises from want of familiarity with 

 Mr. Macdonald's point of view that a doubt suggests 

 itself as to whether we have not here a case, if not of 

 kicking away the ladder before the passenger has arrived 

 at the top, at any rate of removing the supporting 

 framework before the ties and struts of the permanent 

 structure have become entirely consolidated. 



Much in these remarks has assumed a critical form, 

 because after pointing out the excellences that can be 



■ enjoyed by consulting the work itself, it would appear 

 that a reviewer could do best service by discussing the 

 matters that are not so clear. Other more detailed topics 

 might be specified which require further consideration. 

 For instance, students of the modern subject of the 

 relation of radiation to temperature would perhaps be 

 puzzled by § 82, which professes to give a new proof of 

 the Stefan-Boltzmann law ; the transformation of linear 

 scale of the system aether////.? matter, there employed, is 

 a very tempting one, but, unfortunately, the free periods 

 do not seem to correspond. It may be put forward 

 as a reasonable generalisation, subject to only a 

 few striking exceptions, that a book which can be 

 acclaimed as free of discrepancies or obscurities 

 is also to a large extent free of new contributions 

 to knowledge. In the present case, the obvious advances 

 are so important that close attention to the work 

 throughout its whole range cannot safely be neglected. 



J. Larmor. 



NO. 1738, VOL. 67] 



A STUDY IN ALPINE GEOLOGY. 

 Das Sonnwendgebirge itn Unterinnthal. Ein Typus 

 Alpinen Gebirgsbaues. By Dr Franz Wahner. First 

 part. Pp. xii + 350 ; with 96 illustrations in the 

 text, 19 plates and map. (Leipzig and Vienna : F. 

 Deuticke, 1903.) Price 35 marks. 



OF all the labour that has been expended on the 

 fascinating problems of Alpine geology, none, 

 perhaps, has been more fortunate in the manner of its 

 presentation than the work under consideration. A 

 lucid style, fine large type and a wealth of illustration 

 contribute to the enjoyment of an interesting thesis. 

 The weight and bulk of the volume, however, con- 

 stitute a drawback. 



The limited area dealt with by the author comprises 

 the Haiderjoch, Rosan and the Sonnwendjoch ; and 

 the formations range from the Triassic Werfen beds 

 to the Upper Jurassic Aptychenkalk ; but it is with 

 the rocks about the middle of this series that he is 

 mainly concerned. These are classified in the follow- 

 ing, descending, order : — Hornsteinkalk (upper Jura), 

 Hornstein-Breccie, Radiolariengesteine, Rother Lias- 

 kalk [VVeisser Riffkalk, Ober-rhatischer Mergelkalk, 

 Weisser Riffkalk (lower part)], Kossen beds. 



It will be recognised at once that this is an abbre- 

 viation of Pilcher's sequence. The main mass of the 

 Weisser Riffkalk, which has all the characters of a 

 true coral reef, has presented a difficulty to the author 

 from the fact that he has found, in the lower parts, 

 undoubted Rhaetic fossils, and in other parts, which 

 he considers are higher portions of the same group, 

 Lias fossils have been discovered. 



" We are so accustomed to regard the term 

 ' Oberer Dachsteinkalk ' as applied to a Rhaetic rock 

 that it does not seem wise to use it for a group 

 which is in part Rhaetic, in part Liassic. " 



He therefore proposes " Weisser Riffkalk " as a 

 local term, suggestive of the salient character of the 

 group. 



Before presenting the results of his own researches, 

 Dr. Wahner devotes the first 78 pages to the discussion 

 of the geological literature of the Sonnwend district. 

 Commencing with Uttinger in 1819, he passes in re- 

 view practically all that has been written on the 

 subject up to 1900 (in the preface he comments on 

 Ampferrer's paper of 1902). On each paper he makes 

 a few brief explanatory or critical remarks. To Dr. 

 Diener, however, he allots some fifteen pages, occu- 

 pied almost wholly in destructive criticism — " a heap 

 of errors," he says in one place; and he is so irritated 

 by what he regards as Diener's incorrect observations 

 and loose writing that he waxes ironical : " I regret I 

 cannot give any figure of this interesting spot," says 

 Diener, which causes the author to remark, 



"The reader endeavours to keep calm; perhaps 

 D. had no time to make a sketch — but, on second 

 thoughts, a better view is, that what Diener desires 

 (will) to see, nobody can draw " (p. 40). 



With much of the painstaking work of Pilcher, 

 the author is in agreement, but he considers the 



