May 1 6, 1889] 



NATURE 



53 



which call for more careful and precise statement, but on 

 the whole the work is calculated to be useful, and we can 

 recommend it for school use. 



Glimpses of Feverland : of, A Cruise in West African 

 Waters. By Archer P. Crouch, B.A. Oxon. (London: 

 Sampson Low, 1889.) 



In this volume Mr. Crouch presents a record of the 

 impressions made upon him by the land and people of 

 certain portions of West Africa, which he visited in 

 connection with the laying of a cable to put various 

 places, principally French and Portuguese, in telegraphic 

 communication with Europe. A large part of the book 

 is devoted to an account of what he saw during his 

 passage from Accra, on the Gold Coast, to the Portu- 

 guese island of St. Thomd. Afterwards we have a full 

 description of St. Thom(? and St. Paul de Loanda, and in 

 several concluding chapters the author sums up the 

 incidents of his voyage homewards. Mr. Crouch is so 

 good an observer, and has so frank and lively a style, 

 that his narrative, taken as a whole, is fresh and interest- 

 ing, although his subject is often, apart from his treatment 

 of it, dreary enough. He is particularly successful in those 

 passages in which he seeks to give his readers glimpses 

 of native customs and superstitions. It is worthy of note 

 that he has formed a very unfavourable judgment as to 

 the intellectual and moral qualities of the Negro race ; 

 but on this question, with regard to which he differs 

 widely from Mr. Stanley, he perhaps speaks rather more 

 positively than the extent of his experience warrants. 



LETTERS TO THE EDITOR. 



I 77ie Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

 to return, of to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of NATURE. 

 No notice is taken of anonymous communications. ] 



The Meteoritic Theory. 



I H.WE during the past six months been led from the study 

 of our own atmosphere to consider certain phenomena relatinc; 

 on the one hand to the solar atmo-physics, and on the other hand 

 to the evolution of our own globe and its atmosphere. There 

 has thus arisen in my mind a system of cosmo{/ony which has 

 led me, quite independent of Mr. Norman Lockyer's published 

 course of reasoning, back to a meteoric theory that will, 

 I hope, be acceptable to yourself and others. Awaiting 

 '.he preparation of these views fjr publication, I have had 

 occasion to look over the report on the total eclipse of the sun, 

 July 1878 (Professional Papers of the Signal Service, No. i, 

 Washington, 1881). I quote from pp. 49 and 50 some para- 

 graphs to show the connection between views then held and 

 those at which I have recently arrived. 



Washington, April 29. Clevfxand Abbe. 



" Under these circumstances, I could but regard the sugges- 

 tion that occurred to me on July 29 as a slight but important 

 extension and modification of the views previously held. . . . 

 It amounted to saying that a large part of the phenomena of the 

 outer corona is essentially non-solar, having to do with cold 

 meteoric matter that is beyond the solar gaseous atmosphere and 

 is shining by reflected light, . . . rushing on its way to plunge 

 into the sun's atmosphere, where, within a few hours, it would be 

 <lissipated. . . . That these lieams were due to wholly new 

 meteor streams . . . now for the first time approachin<j the sun. 

 ... I am now inclined to extend this view to very many of the 

 radiating dark artd bright lines observed during eclipses, and 

 would explain most of them as due to brightly iduminated 

 groups and streams of meteors and to large meteors followed by 

 trains. . . . Those meteors that enter the solar atmosphere and 

 become incandescent will of course shine with a greitly in- 

 creased splendour, and thus constitute a portion of the inner 

 corona ; these thus show us the limit of the gaseous atmosphere 

 «f the sun, . . . The extreme limit may bo located at a distance 



of five minutes (of arc) above the sun's surface, and is very 

 likely to be less than this. . . . Meteors glow as shooting-stars 

 when tliey strike our atmosphere with a relative velocity of from 

 twenty to forty miles per second, and at an altitude of about one 

 hundred miles, where the density of the atmosphere may be 

 about 3 X lo"" times that which prevails at the surface. Now 

 these same meteors will, when they have approached to within 

 130,000 miles of the sun's surface, have a momentum at least a 

 hundred times greater than that with which they enter the outer 

 limit of the earth's atmosphere ; therefore we are allowed to 

 assume the density of the outer limit of the supposed solar 

 atmosphere to be but the hun Jredth part of that of the earth, 

 or 3 X io~" ; this gives us for the base of the solar atmo- 

 sphere a density and a pressure quite within plausible bounds." 



The Structure and Distribution of Coral Reefs. 



Thosk who have read the additional appendix in the edition 

 just published of Mr. Darwin's work on coral reefs will doubt- 

 less have observed that whilst the recent evidence there pro- 

 duced against the theory of subsidence lies chiefly in observations 

 on living reefs in the Florida seas, in the Western Pacific, and in 

 the Indian Ocean, the new testimony advanced on behalf of the 

 theory is in the main indirect in bearing, and is based ou 

 assumptions that have yet to be proved. 



Referring to the latter evidence in the order of mention, I come 

 first to the 90-fathom neef off Socotra, a reef that is assumed to 

 have been lowered by a movement of subsidence into its present 

 position. So defective is our knowledge of the depths at which 

 coral reefs may grow, and so incomplete is our acquaintance 

 with the complex agencies that combine to produce a coral reef 

 or to limit and prevent its growth, that the inference respecting 

 tlie depth of the Socotra reef may be truly characterized as 

 based on an unproved assumption. At present our acquaintance 

 with the fauna of the submarine slopes of tropical islands in the 

 Indian and Pacific Oceans, between the depths of 20 and 100 

 fathoms, is of the scantiest description ; and we are not in a 

 position to hazard even a guess on the subject, much less to 

 assume that an island like Socotra has experienced a movement 

 of subsidence because it possesses a reef "submerged in some 

 places to a depth of over 90 fathoms." It is owing to our 

 ignorance of the fauna in these depths that it has not been 

 possible to identify the great numbers of minute molluscan shells, 

 which occurred in the upraised post-Tertiary muds discovered 

 by me in the Solomon Islands ; and it is of the lack of such know- 

 ledge that Prof. K. Martin in his recent great work on the 

 Tertiary formations of Java naturally complains. Surely, when 

 the biologist is fain to acknowledge his want of acquaintance 

 with the matter, and when as a consequence the palaeontologist 

 and the geologist have to bring their labours to a standstill from 

 the lack of comparative material, it seems rather dangerous for 

 the coral reef speculator to assume what has never been properly 

 examined. 



If, therefore, we have yet to determine the limit of depth of 

 the growth of coral reefs, we are scarcely in a position to advance 

 as evidence in behalf of subsidence the thickness of certain up- 

 raised beds of coral limestone in the West Indies and in the 

 Sandwich Islands. Even if such evidence should be ascertained 

 to be valid in itself, it must be remembered that Mr. Murray in 

 his theory places no limit to the possible thickness of coral reefs, 

 and that in the outward growth of a reef a considerable thickness 

 may be produced. There was, in truth, no circumstance more 

 impressed on my mind in the Cocos-Keeling Islands than the 

 seaward extension of ciral reefs. 



Once more, however, I would impress on future investigators 

 the extent of our ignorance of the depths in which coral reefs 

 may form. In one of my papers (Proc. Roy. Soc. Edin., 1885- 

 86, p. 887) I have pointed out that the estimates of observers in 

 different regions vary between 5 and 40 fathoms. It is also 

 singular how different observers may vary in the conclusions they 

 draw from the same lines of soundings. The soundings off 

 Keeling Atnll were made by Captain Fitzroy himself, and he 

 places the limit of depth at 7 fathoms ("Voy. Adventure and 

 Beagle" ii. 634) ; whilst his companion, Mr. Darwin, judging 

 from the same soundings, concluded that it lay between 12 and 

 20 fathoms. In truth, as long since pointed out by Prof. 

 .Semper, the whole question of the depth of the reef-coral zone 

 has never been methodically investigated. It never occurred to 

 Mr. Darwin or Prof. Dana that coral reefs might grow in depths 

 beyond the belt of sand that apparently limited their growth. Yet 



