April 2"], 1876] 



NATURE 



505 



ing instruments the gauges lent by Sir Joseph Whitworth 

 are remarkable for their delicacy. With one of these, for 

 measuring the bore of guns, differences of «ne-ten-thou- 

 sandth of an inch can be measured. There is another, 

 moreover, by means of which a quantity so minute as one- 

 millionth can be grasped. The apparatuses which Joule 

 employed in ascertaining the mechanical equivalent of 

 heat, are among the collection. 



The field of magnetism and electricity is now a very 

 vast one, and in the exhibition it is represented by a cor- 

 respondingly large variety of apparatus. A peculiar halo 

 of interest gathers round the instruments, many of them 

 so simple and homely, with which Faraday worked out his 

 fruitful ideas. Among old electric machines is one with 

 two glass cylinders, one of which is covered with sealing- 

 wax, so as to obtain both positive and negative electricity ; 

 there is also Naime's early electric machine with glass 

 globe, Armstrong's hydro-electric machine, &c. Volta's 

 electric lamp is exhibited for lighting gas by means of the 

 electric spark. There is an endless variety of batteries, 

 and the numerous Holz and other electric machines 

 exhibited will afford material for careful study, as 

 also the novel forms of magneto-electric and other 

 machines which have of late years multiplied so 

 fast. Here may be found apparatus for regulating the 

 time and place of an electric discharge ; apparatus for 

 accumulating electricity ; apparatus for observing the 

 effects of discharge of accumulated electricity ; appa- 

 ratus for producing, and apparatus for observing, eftects 

 of continuous electric currents ; apparatus for measuring 

 the strength of electric currents, and apparatus for mea- 

 suring resistance, and so on. In the telegraphic depart- 

 ment there is a complete historical collection which must 

 be of great interest not only to electricians and tele- 

 graphists, but to the general public, illustrating the 

 progress of the electric telegraph from the time when 

 the first idea of it was crudely embodied, down to 

 the present time. This collection includes, of course, 

 all the classical apparatus which belonged to Wheat- 

 stone and Cooke, among which is the original 

 Wheatstone Bridge. Many will be interested in seeing 

 the instruments that were used on board the Great 

 Eastern in laying the Atlantic Cable. There are copies 

 of the first German telegraphic apparatus (Goemmer- 

 ing's), and the first needle telegraph (Schelling's) ; the 

 electro-magnetic telegraph apparatus used by Gauss and 

 Weber in Gottingen, from 1833 to 1838, &c., &c. 



We must here desist for the present, though the majority 

 of the sections are still unvisited. It may be understood, 

 even from these hasty and imperfect notes — but in any 

 case, the reader may soon convince himself by personal 

 inspection — how rich and varied is the collection now in 

 course of completion, and how ample is the feast therein 

 provided for those who feel in any measure drawn to the 

 " beautiful and true " in science. 



The date of opening of the exhibition is still uncertain. 

 It is hoped that her Majesty will grace the occasion with 

 her presence, and conduct the opening ceremony. Some 

 of the galleries of the exhibition will probably be lighted 

 in the evenings with the electric light, and a considerable 

 portion of the apparatus, it is intended, will be kept in 

 motion. 



GREEN'S GEOLOGY 



Geology for Students and General Readers. Part I. 



Physical Geology. By A. H. Green, M.A., F.G.S., 



Professor of Geology in the Yorkshire College of 



Science, &c. (London : Daldy, Isbister, and Co., 1876.) 



THE progress of geological research in every quarter 

 of the globe is exceedingly rapid, and discoveries of 

 new processes of investigation, leading to the opening up 

 of fresh lines of thought in connection with the science, are 

 constantly taking place. Hence, in spite of the acknow- 

 ledged excellenceof someof the existing manuals of geology, 

 such as those of Lyell and Jukes, we cannot but hail with 

 pleasure the appearance of a new text-book of the science 

 — especially of one which, like the present work, is not 

 a mere epitome of one or other of the standard treatises 

 just referred to, but which aims at some originality in its 

 arrangement and mode of treatment of the subject- 

 Prof. Green may be congratulated on having written a 

 work embodying a vast amount of valuable information, 

 which is presented in a very clear and readable form. 



Of the two classes for whom Prof. Green writes, we 

 think the " general readers " are those for whom his work 

 is best adapted. Some of the chapters, such as the 

 ninth, which is entitled, " How the rocks came into the 

 positions in which we now find them," and the tenth, of 

 which the heading is, " How the present surface of the 

 ground has been produced," are models of clear and 

 accurate description, and of logical and forcible reason- 

 ing ; they are evidently written by a man with a thorough 

 acquaintance with his subject, and no little enthusiasm, 

 for it to boot. We may, perhaps, demur to the confident 

 tone and the sometimes off-hand manner with which our 

 author disposes of the objections of those who differ from 

 himself on some of the questions discussed ; yet we can- 

 not but feel that the conclusions at which he has arrived 

 and which he so clearly states, are the result of inde- 

 pendent observation and personal conviction, and are 

 not merely adopted at second-hand. While reading many 

 parts of this work, it is impossible to avoid the conscious- 

 ness that we are following the pleadings of an advocate, 

 and not the expositions of a judge ; yet the arguments 

 are brought forward with such lucidity and earnestness, 

 that we accept the work as embodying the ablest expo- 

 sition yet offered to us, of the views of that school of 

 geologists to which Prof. Green belongs. Occasionally, 

 however, the author is so carried away by his enthusiasm 

 in behalf of favourite doctrines, that his confidence be- 

 comes something very like arrogance, as in the follow- 

 ing passage, with which he concludes his chapter on 

 Denudation : — 



" The reader will do well to compare with the theory 

 of surface- sculpture upheld in the preceding memoirs, 

 chapter xbc of the late Prof. Philhps' ' Geology of the 

 Valley of the Thames.' Elegant and ingenious as is the 

 explanation there put forward, there is about it an un- 

 satisfactory vagueness and want of definition, which con- 

 trasts strongly with the sharp precision and logical cohe- 

 rence of the views on the subject of which a sketch has 

 teen attempted in the preceding pages, and which are 

 steadily gaining ground among modem geologists." 



In keeping apart from the other portion of his work 

 purely speculative questions, and treating of them in two 

 chapters at the end of the volume, we think the author 



