August 1 6, 1883] 



NA TURE 



365 



the kind of action we are considering. First, a little work 

 spent in pulling the trigger releases a strong spring in the 

 lock, and brings about a smart blow with the hammer. 

 This blow liberates the explosive energy of the percussion 

 cap, which in its turn fires the powder. Thus we have a 

 series of processes in which the running down of a small 

 quantity of energy gives opportunity for the running down 

 of a larger." 



This is only one illustration out of many which might 

 be given. In fine the student of physics will find in this 

 volume an accurate and clearly cut map of the various 

 districts for the more minute details of which he must of 

 course be referred to other guides. B. S. 



Formulaire Pratique de UElectricien, Par E. Hospitalier, 

 Premiere Annee, 1883. (Paris: G. Masson.) 



In his "Formulaire Pratique de 1' Electricien " M. Hos- 

 pitalier has supplied us with a work which cannot fail to 

 be of value as a convenient book of reference. It is 

 divided into five parts. In the first are stated as briefly 

 as possible those general principles with which every one 

 who is in any way connected with electrical nutters should 

 be familiar. In the second is given the derivation of the 

 electrical and magnetic units, with which are tabulated 

 all the arbitrary units that have been or are at all gene- 

 rally used. In the third chapter almost every instrument 

 and method that may be employed for making any mea- 

 surement which an electrician is likely to require is 

 mentioned, and when necessary explained by a figure. 

 Though it must have been difficult to decide what to 

 include and what to omit, surely considering the growing 

 importance of "diagrams" so very useful an instrument 

 as Amsler's planimeter might have been mentioned. 



The fourth chapter, which in quantity is equal to all 

 the rest of the book put together, contains a large amount 

 of miscellaneous information. After giving the usual 

 mathematical tables and formulae, and several tables of 

 the physical properties of bodies, the author treats in 

 succession of batteries, accumulators, electro-metallurgy, 

 thermo-electricity, dynamo-machines, and motors, electric 

 lighting, the telegraph, and telephone. 



The fifth chapter consists of a few pages, in which the 

 composition of various alloys, cements, and varnishes, and 

 a few manipulative processes are described. This part 

 might and no doubt will be improved. For instance, a 

 troublesome process of amalgamating iron is given, but 

 no mention is made of the well known property that 

 sodium possesses of making mercury wet iron or 

 platinum. 



There can be no doubt that both in the laboratory and 

 in the workshop this will be found one of the most handy 

 and complete books of reference existing. C. V. 15. 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts, 

 No notice is taken of anonymous communications. 



[ The Editor urgently requests correspondents to keep their letters 

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

 that it is impossible otherwise to insure the appearance even 

 of communications containing interesting and novel facts.] 



" Elevation and Subsidence " 



In an article in last week's Nature on "Elevation and Subsi- 

 dence" (p. 323), Darwin's theory on the formation of coral islands 

 is contrasted with mine, and it is apparently assumed that lay 

 theory is opposed to subsidence in those regions of the ocean 

 where atolls and barrier reefs are situated. 



I am not aware I have ever contended for this, but as several 

 writers have lately attributed this opinion to me it may he as 

 well to re-tate the position. My view is that the characteristic 

 form of barrier reefs and atolls is in no way dependent on sub- 

 sidence ; that subsidence is not the cause of their peculiar fea- 

 tures ; that these reefs may be met with indifferently in station- 



ary areas, in areas of subsidence, and in areas of elevation ; and 

 that elevation and subsidence only modify in a minor way the 

 appearance of these islands. 



All naturalists will be willing to acknowledge that Darwin's 

 theory is "simple and admirable," but I do nit think it will be 

 generally admitted by those who have carefully examined coral 

 reefs in recent years that it " accounts satisfactorily for all the 

 observed phenomena of coral growth." 



According to the explanation given by Darwin, the founda- 

 tions of the coral reef sink gradually, and the corals, as gradually, 

 build up the reef to the level of the waves. In this way these 

 interesting coral islands are slowly developed. 



It appears to me that the chief phenomena of barrier reefs and 

 atolls are more satisfactorily accounted for in another way : — 



1. By a physiological fact — the very vigorous growth of the 

 reef-forming species on the outer or seaward face of the reef 

 where there is abundance of food, and the much less vigorous 

 growth and even death of these species on the inner parts of the 

 reefs and in the lagoons, where there is much less food, and 

 where there are other conditions inimical to growth. 



2. By a physical and chemical fact — the removal of lime in 

 suspension and in solutio 1 from the inner portions of the reefs 

 and from the lagoons, where much dead coral is exposed to the 

 action of sea water containing carbonic acid — the result being 

 the formation, the deepening, and the widening of lagoons and 

 lagoon channels. 



My theory is represented as demanding "290 volcanic peaks 

 at the sea level in the Pacific coral area alone." 



What 1 have endeavoured to show is that the sum of all the 

 agencies at work above the sea tends to reduce volcanic cones 

 down to twenty or thirty fathoms beneath the waves, and the 

 sum of all the agencies at work under the sea level tends to 

 build up volcanic cones to within twenty or thirty fathoms of tbe 

 surface. 



In both cases banks are formed on which reef building corals 

 grow and eventually develop into atolls. The nearer the summit 

 of the cone is to the sea level, whether above or below it, the 

 more rapid is the formation of the bank. 



Atolls, as we now see them, should, according to Darwin's theory, 

 be situated on the summits of gigantic pillars of coral, which are 

 probably higher (or deeper) the greater the diameter of the atoll. 

 These pillars should rest on volcanic cones or peaks of conti- 

 nental land ; and in the " Pacific coral area alone " should mark 

 the spots where "290 peaks" have subsided. Where are tbe 

 soundings which corroborate this part of Darwin's theory ? 



John Murray 



Challenger Office, 32, Queen Street, Edinburgh, August 6 



In his article on "Elevation and Subsidence" (Nature, 

 vol. xxviii. p. 323) Mr. Starkie Gardner has given some very 

 interesting new illustrations, drawn from observations of bis own 

 upon lava-fields in Iceland, where it is his belief that tracts have 

 sunk owing to the mere weight of lava poured over them. But 

 there are several places in his reasoning upon the general ques- 

 tion of the condition of the earth's interior where he appears to 

 argue upon the supposition that pressure by itself can be the 

 cause of heat, and consequently of an increase of temperature 

 among deeply buried rocks. This, however, as those who are 

 acquainted with the science of energy will know, is clearly a 

 mistake. It is only where pressure has produced > v otion, and 

 that motion has been destroyed as visible motion in a mass of 

 matter, and transformed into motion among the molecules of the 

 matter, that the mass can be heated thereby. 



Supposing that rocks at a considerable depth, and therefore 

 under great pressure, are hot enough to be melted, it does not 

 follow that the pres-ure is the cause either of the high tempera- 

 ture or of the fu> ion. We must look for some other cause for 

 that high temperature and fusion, and this can only be guessed 

 at. But it probably arises from the earth having once been 

 an incandescent body — a little sun — which is now gradually 

 cooling. 



I have been led to make these remarks because Mr. Starkie 

 Gardner has referred to a publication of my own with greater 

 approbation than it perhaps deserves ; but at the same time he 

 says that the views he has put forward in his article present some 

 important differences from mine. I wish therefore to be allowtd 

 to say that what I have now mentioned, and the consequences 

 which he has deduced from it, are the only important points in 

 which I should disagree with him. O. Fisher 



Harlton, Cambridge, August 13 



