.Vov. I, 1883] 



NATURE 



OUR BOOK SHELF 

 Elemcnti di Fisica. Vol. IV., EUttriciti e Magnetismo. 



By Prof. Antonio Roiti. (Florence, 1SS3.) 

 Surely, and not slowly, the views of Thomson, Maxwell, 

 and the modern electricians generally are finding accept- 

 ance throughout the Continent. The absolutely unani- 

 mous acceptance of the British Association's system of 

 electrical units since the indorsement of that system by 

 the Paris Congress of iSSt has proved the immense gain 

 to the electrical world of having a uniform means of ex- 

 pressing electrical quantities, and has compelled elec- 

 tricians not only to read but to comprehend the writings 

 of the pioneers of this most important reform. The work 

 now before us for review, though professing to be but a 

 text-book for use in the lyceums and schools of Italy, 

 gives ample evidence that its author. Prof Roiti, of the 

 Royal Institute of Higher Studies in Florence, is not 

 only abreast of all the latest developments of electricity, 

 but that he has mastered the theory also. Few text-books 

 of its size have we seen that will compare favourably with 

 Prof. Roiti's little volume of 356 duodecimo pages. The 

 faults which have been hitherto so conspicuous in most 

 of the Continental text-books on electricity are in this 

 work conspicuously absent. As an example we may 

 refer to the author's treatment of the relation between the 

 capacities, potentials, and charges of similar conductors. 

 The elementary theory of the magnetic shell and that 

 of the mutual potential of two magnetic shells are 

 neatly expounded in pages 131 to 133. The absolute 

 electrometer and the quadrant electrometer of Sir W. 

 Thomson are both described, and illustrative figures 

 given. The system of absolute and derived (C.G.S.) 

 units, and that of the practical units of electric quantities 

 based upon them, are explained at length on pages 204-5. 

 There is a short chapter on the electric light, and 

 another on electric motors, in which the ancllo elettro- 

 mag)tctico di Paciiwtii is described, the author remark- 

 ing with emphasis that it contained the germ of almost 

 all the machines by which the marvellous strides recently 

 made in the applications of electricity have been achieved. 

 The experiments of Ueprez at Paris on the electric 

 transmission of power, and the economic questions 

 involved are also touched upon. Crookes's researches 

 on "radiant matter" are mentioned and illustrated. 

 Amongst points of novelty may be mentioned Pellat's 

 method of measuring the electromotive force due to 

 polarisation, which has not yet, we believe, found its way 

 into any English text-book. Two points of criticism we 

 have to offer in conclusion. The first is that the author 

 defines electric tension as identical with the tXsctnc force, 

 equal to 4 7r times the surface density of the charge, in- 

 stead of defining it, in the sense of Faraday and Maxwell, 

 as the stress on the dielectric, which is proportional to 

 the square of the surface density, and therefore propor- 

 tional also to the square of the electric force or electro- 

 motive intensity at the point of the surface considered. 

 The only other complaint we have to make of the work — 

 and this docs not detract greatly from Us value— is that 

 the author does not acknowledge the sources from wii'.oK 

 some of ills descriptions and cuts are taken. S. P. T. 



Dr. H. G. Bromis Klassen und Ordniingeii des Thier- 



Reichs, luissenschaftlich dar^eslt-llt in IVort und Bild. 



Erster Band, Protozoa. Neu bearbeitet von Dr. O. 



Biitschli. (Leipzig and Heidelberg: C. F. Winter, 



1880-S3.) 

 The first nineteen 'parts of this new edition of vol i. of 

 Dr. Bronn's well known and important work on the classes 

 and orders of animals, nearly completing the volume, 

 prove that Prof Butschli has spared no pains to keep 

 It up to the most modern investigations of the Protozoa. 

 In no one division of the animal kingdom has observation 

 gone so hand in hand with discovery as in this, the lowest 



of her classes. Glancing at the portion treating of the 

 Gregarinida, what strides have been made in our know- 

 ledge of these forms within the last ten years. Adopting 

 Leuckart's titles for the class of Sporozoa, under which are 

 the sub-classes Gregarinida, Coccidia, Myxosporidia, and 

 Sarcosporidia, we find 137 pages and eight plates 

 crowded with figures devoted to a sketch of the charac- 

 teristics of the class with diagnoses of the genera and the 

 number of species, and references to the places where 

 fuller details of these latter will be found. The illustra- 

 tions are clear and effective, and copied from every avail- 

 able source. The bibliography appears to be well to date, 

 and this volume when complete will be an indispensable 

 handbook for the student of the lower forms of animal 

 life. 



LETTERS TO THE EDITOR 



[ Tlie EJUor docs not hold himself resfonsiblefor opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond zvith the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



[ The Editor urgently requests con espondents to keep their let 'ers 

 as short as possible. The pressure on his space is so great 

 that it is impossible otherwise to insjtre the appearance even 

 of coniiiiunications containing interesting and novel facts.'] 



"Elevation and Subsidence" 



The view that the glacial subsidence was due to the pressure 

 of the accumulating land ice, has been accompanied with the 

 coroUiry that subsequent elevation was due to the removal of 

 this pressure by the melting of the ice ; but though I think the 

 first is true, the corollai-y is not so, in England .it least. 



In my memoir "On the Newer Pliocene Period in England" 

 (Quart. Journ. Geol. Soc.iox 1S80, p. 457, and 1SS2, p. 667^, I 

 have endeavoured to show how the inclination of this couiitiy 

 changed during the progress of the major glaciation, and the 

 flow of the land ice from the mountain districts to the sea 

 altered in accordance therewith, as well as pointed out (p. 709) 

 the connection of this ch.inge of inclination with the accumula- 

 tion of the land ice on the mountain districts; but I have al o 

 traced in detail in it how the east side of England rose to an 

 extent that brought Norfolk and Suffolk from a submergence of 

 more than 300 feet to their present level at least, and Essex 

 proportionately so, while the land ice continued to push over 

 the sea-bed of sand and gravel, as this rose into land, covering 

 it w ilh its moraine, until by this ri^e the easterly movement of 

 the ice was arrested, while the west and south of England still 

 remained to a great extent submerged. Since that memoir was 

 published, Mr. David has in the same journal described the 

 glacial clay which represents the moraine of the Wehh land ice 

 in East Glamorganshire, itself ««covered by any marine deposit, 

 as covering beds of stratified sand and gravel, which, from their 

 containing many chalk flints, can be only the bottom of the 

 antecedent sea, as low down as 80 feet above Ordnance datum. 

 When this is compared vith the evidence of more tban 1300 

 feet of submergence afforded by the shell bearing gravels of 

 North Wales ; of 700 feet afforded by the Gloucestershire 

 gravels to the east ; and of between 500 and 6o3 feet afforded 

 by the gravels of Devon to the south of Glamorganshire, it be- 

 comes ev'dent that the amount of rise which took place in the 

 west of England before the land ice began to retreat « as even 

 greater than in East Anglia. It is to subterranean movcmenls 

 ciigciij^..,! i,y (ijJ5 pressure, and not to its removal, that the rise 

 m England seems lo >„.. .- y,,„^ ^een due ; and I have given 

 several sections in tbis memoir in iiuiai.„.>- . -^.'''o abrupt and 

 violent character of the upthrows connected with it. 



Although in this memoir I remarked upon the coincidence of 

 the westerly increment in the great submergence with the aug- 

 menting quantity of the land ice on Cumberland, Westmoreland, 

 and Wales, as the major glaciation went on, yet this coincidence 

 between augmenting land ice and .submergence is, I now see, 

 more complete than had then occurred to me ; for though I 

 described the evidences that show the passage from the Crag 

 to the gUacial marine beds of Norfolk and Suffolk to have been 

 accompanied by a northerly subsidence which submerged the 

 valley of the Crag river, in the north of th'e former ciunty, 

 while the other extremity of its estuary (iu East Suffolk) was 

 elevated, so that idands formed of Crag beds came there into 



