78 



NATURE 



[Nov. 23, 1876 



On the Internal Fluidity of the Earth 

 The question of the solidification of the crust of the earth 

 from the fluid interior nucleus, as referred to by Mr. Mathieu 

 Williams, in Nature, vol. xv. p. 5, is one which has been long 

 since fully discussed in my papers in the Philosophical Transac- 

 tions, the Atlatitis, vol. i. , and in a paper of which an abstract 

 appears in the Report of the British Association for 1856. As 

 far as I am aware, no person has controverted my conclusions as 

 to the process of solidification of the earth. The results are, in 

 the mam, somewhat similar to those so admirably illustrated and 

 enforced by Mr. Robert Mallet, and also such as Mr. Williams 

 upholds in this journal. 



In articles 6 and 7 of my "Researches in Terrestrial Physic?," 

 Part I, this subject is discussed as a problem of fluid equi- 

 librium, and the conclusion is there deduced that the fluid 

 interior mass of the earth must consist of spheroidal strata of 

 equal density, the density of each stratum increasing from the 

 surface to the centre of the nucleus. The mode in which this 

 arrangement of the fluid matter would favour the formation of a 

 solid crust is pointed out. In Part 2 Section III., the probable 

 law of density of these fluid strata is discussed. In Section IV. 

 the shape of these strata is investigated, and also that of the 

 inner surface of the shell or crust. It is shown independently of 

 the law of density that the least ellipticity of this inner surface 

 of the crust cannot be less than the ellipticity of its outer surface. 

 A similar result was soon afterwards enunciated by Plana in a 

 paper in the Aitronomische Nachrichten. In the same section 

 the theory of a solid nucleus in the earth originally proposed by 

 Poisson, is examined and shown to be incompatible with physical 

 laws. 



Owing to the pointed manner in which Sir William Thorason 

 invited discussion in a previous number of Nature, I ventured 

 to controvert his views as to the rigidity of the earth in a paper 

 inserted at p. 288, vol. v. of this journal. Never at any time 

 have I had even a doubt as to the untenable character of Sir 

 William Thomson's views regarding ihe solidity of the earth. 



In again reiterating this opinion in Nature, vol. ix. p. 103, 

 a reference to my paper was given, in which vol. vii. p. 285, is 

 misprinted for vol. v. p. 288. 



In his address at Glasgow Sir William Thomson, while main- 

 taining his opinion as to the eartli's solidity, appears to have 

 seen the weakness of some of his former arguments by calling on 

 his hearers (Natuiie, vol. xiv. p. 428) to erase whdle para- 

 graphs of his paper on the Rigidity of the Earth, in the Philo- 

 sophical Transactions. At the same passage of his address he 

 refers to a hint from Prof. Newcomb, that viscosity might suffice 

 to render precession and nutation, the same as if the earth were 

 rigid. "This," he says, "I would not for a moment adnnit, any 

 more than when it was ji?rj/ put forward by Delaunay." The 

 Comptes Rendus of the Academy of Sciences of Paris for March 6, 

 1871, contains a paper in which my priority on this pomt is 

 clearly established. In Nature, vol. iii. p. 420, the following 

 statement occurs : — "Paris Academy of Sciences, March 13. — 

 M. Delaunay read a declaration stating that he acknowledged 

 that Mr. Hennessy had used the same arguments as himself 

 against Mr. Hopkins' theory relative to the fluidity of the interior 

 parts of the earth." 



I am willing to believe that Sir William Thomson had neither 

 seen the Comptcs Jiendus nor the paragraph in Nature just 

 quoted, but it is to be regretted that a presidential address 

 should contain an erroneous statement on a point of recent scien- 

 tific history, especially when the error could be avoided by a 

 glance at the most widely knov/n scientific publications. 



All through the portion of his address which refers to the 

 earth's structure Sir William Thomson assumes that the views of 

 Mr. Ilopkirs are established and admitted. A reference to some 

 of the past volumes of this journal alone shows the inadmissi- 

 bility of such an assumption. At pp. 45 and 182 of vol. iv. and 

 elsewhere Mr. Hopkins' views are distinctly controverted on 

 mechanical, physical, and geological grounds. 



It appears that in the discussion on my p.^per in the Academy 

 of Sciences of Paris, in which s-ome of the most eminent mathe- 

 maticians and geologists of France took part, not one of them 

 adopted Mr. Hopkins' " Discovery of the earth's sohdity." As 

 far as I am aware, this "discovery" is not adopted anywhere on 

 the continent of Europe. I have studied with as much care and 

 attention as I could give to them, the mathematical and physical 

 researches of Mr. Hopkins and Sir William Thomson relative to 

 this subject, and for reasons already partly unfolded in this 

 journal at vol. v. p. 288 and vol. iv. p. 182, I continue to firmly 



adhere to the almost diametrically opposite conclusions long 

 since enunciated in the publications referred to at the outset of 

 this communication. Henry Hknnessv 



Royal College of Science, Dublin 



The Age of the Rocks of Charnwood Forest 



I see that in Mr. Woodward's "Geology of England and 

 Wales," recently published, the rocks of Charnwood Forest, in 

 Leicestershire, ai^(with some hesitation) referred to the"Laur- 

 entian " series. Prof. Ansted and Dr. HoU being quoted as 

 authorities. The reviewer in the recent number of the Saturday 

 Review adopts the same opinion ; at the same time it is proper to 

 add that Mr. Woodward states in another place (p. 31) that the 

 Charnwood Forest rocks "may be of Cambrian age," so that the 

 reader is left to take his choice. 



For my part I confess to being at a loss to understand on what 

 grounds these old rocks can be referred to any other than the 

 Cambrian period. The evidence in any case is small, but what 

 there is points to this conclusion. 



In the first place it ought to be remembered that the age of 

 these rocks was first indicated by Prof. Sedgwick, whose opinion 

 on such a question should not be disregarded unless on very sub- 

 stantial grounds. Sedgwick's opinion of their age was founded 

 almost entirely on lithological grounds, and no one was better 

 qualified to recognise the representatives of the Welsh Cam- 

 brians, though rising up isolated amongst much newer formations 

 in the heart of England. Prof. Jukes, in his description of the 

 geology of Charnwood Forest, appended to Porter's " History," 

 adopted the same view, in which the officers of the Geological Sur- 

 vey, including the present Director-General, who mr^de a personal 

 examination of the forest rocks, c mcurred (see "Geology of the 

 Leicestershire Coal Field," Mem. Geol. Survey, i860). I am 

 not aware that they have changed their views owing to what 

 has been since written on the subject. 



As regards the determination of the age of these rocks, if it is 

 impossible to prove them to be of Cambrian age, there are very 

 good grounds for conclyding they are not of " Laurentian " agf, 

 assuming that term to refer to the fundamenial gneiss of the north- 

 west Highlands and Isles of Scotland. These rocks consist, 

 according to the description of Murchison, of coarsely crystalline 

 gneiss, full of granite veins. They are everywhere intensely meta- 

 morphosed. Now, this is far from being the case with the 

 Charnwood Forest rocks. Generally they are no more meta- 

 m.orphosed than are the Cambrian beds of the Longmynd, or 

 of Llanberis. True "gneiss" is very exceptional, and meta- 

 morphic action is quite local, and is chiefly confined to one 

 district. Any argument, therefore, drawn from lithological re- 

 semblance to the rocks of the typical district entirely iails ; and 

 I cannot admit that the occurrence of rocks (sjenite, &c. ) resem- 

 bling those of the Malvern Hills, is of any force in this question, 

 as it is very far from having been proved that the Malvern Rocks 

 are of Lanrentian age. 



As regards evidence founded on organic remains, it is of the 

 most meagre kind, but whatever the obscure markings on the 

 slates of charnwood may really be, they are certainly not those 

 of eozoon. From whatever side, therefore, the question is viewed, 

 there appears to be no good ground tor departing from the view 

 regarding the age of these rocks originally adopted by Sedgwick. 



Edward Hull 



Geological Survey Office, Dublin, November 3 



Mind and Matter 



Mr. Spalding in his critique on Maudsley's " Physiology of 

 Mind" (Nature, vol. xiv. p. 541), while admitting that "the 

 dependence of consciousness on nervous organisation, seemed," 

 by the science of nerve physiolojjy, "to be fairly established,'" 

 stated that the difficulty of conceiving how consciousness stood 

 related to the material organism, was a difficulty which had not 

 yet been overcome. 



Might not this problem be solved somewhat thus : — It is as 

 easy to predicate subjectivity (or susceptibility to consciousness) 

 of one entity called matter, as of another entity called soul or 

 spirit. It is no more difficult to conceive of matter being sub- 

 jective than of spirit being subjective. 



Again, energy accompanies matter in all its forms, and yet 



