July 7, 1881] 



NATURE 



231 



can exist. This may to some extent account for the reluctance 

 which English capitalists feel in embarking in the manuf^icture 

 of artificial colouring matters. That England possesses both in 

 the scientific and in the practical direction ability equal to the 

 occasion none can doubt. But be that as it may, the whole 

 honour of the discovery of artificial indigo belongs to Germany 

 and to the distin;iuished chemist Prof. Adolf Uaeyer, whilst 

 towards the solution of the difficult problem of its economic 

 manuf.icture, the first successful steps have been taken by Dr. 

 Caro and the Baden Aniline and Soda Works at Mannheim. 



H. E. R. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE 



Thb Linacre Chair of Physiology and Anatomy, lately held 

 by Dr. RoUeston, and practically a chair of comparative 

 zoology, will now be split into two, being succeeded by chairs 

 of anatomy proper and physiology proper, with a more direct 

 relation to the teaching of those subjects as part of a preliminary 

 medical education, as was intended by Dr Linacre. 



Dr. Oliver J. Lodge has been appointed to the Lyon Jones 

 Professorship of Experimental Physics and Mathematics in 

 University College, Liverpool, by the Councils of that College 

 and of the Liverpool Royal Infirmary School of Medicine. Prof. 

 Lodge has been some time Assistant Professor of Physics at 

 University College, London, and is the author of a work on 

 elementary mechanics and various papers of original research. 



SOCIETIES AND ACADEMIES 

 London 



Royal Society, June 16. — "On the Stresses caused in the 

 Interior of the Earth by the Weight of Continents and Mountains, " 

 by G. H. Darwin, F.R.S. 



The existence of dry land proves that the earth's surface is not 

 a figure of equilibrium appropriate for the diurnal rotation. 

 Hence the interior of the earth must be in a state of stress, 

 and as the land does not sink in, nor the sea-bed rise up, the 

 materials of which the earth is made must be strong enough to 

 bear this stress. 



We are thus led to inquire how the stresses are distributed in 

 the earth's mass, and what are magnitudes of the stresses. 



In this paper a problem of the kind indicated is solved, by the 

 use of certain results obtained by Sir William Thomson, for the 

 case of a homogeneous incompressible elastic sphere, and the 

 results are applied to the case of the earth. 



If the earth be formed of a crust with a semi-fluid interior 

 the stresses in that crust must be greater than if the whole mass 

 be solid, far greater if the crust be thin. 



The strength of an elastic solid is estimated by the difference 

 between the greatest and least principal stresses, when it is on 

 the point of breaking, or, according to the phraseology adopted, 

 by the breaking stress-difference. The most familiar examples 

 of breaking stress-difference are when a wire or rod is stretched 

 or crushed until it breaks ; then the breaking load divided by the 

 area of the section of the wire or rod is the measure of the 

 strength of the material. Stress-difference is thus to be measured 

 by tons per square inch. 



The problem is only solved for the class of inequalities called 

 zonal harmonics ; these consist of a number of waves running 

 rotmd the globes in parallels of latitude. The number of waves 

 is determined by the order of the harmonic. In application to 

 the earth the equator referred to may be any great circle, and is 

 not necessarily the terrestrial equator. The second harmonic has 

 only a single wave, and consists of an elevation at an equator 

 and depression at the pole ; this constitutes ellipticity of the 

 spheroid. An harmonic of a high order may be described as a 

 series of mountain chains, with intervening valleys, running 

 round the globe in parallels of latitude, estimated with reference 

 to the chosen equator. 



_ In the case of the second harmonic it appears that the stress- 

 difference rises to a maximum at the centre of the globe, and is 

 constant all over the surface. The central stress-difference is 

 eight times as great as the superficial. 



Amongst other examples it is shown that if the homogeneous 

 earth, with ellipticity -^\r,, were to stop rotating, the central 

 stress-difference would be thirty-three tons per square inch, and 

 it would rupture if made of any material excepting the finest 

 steel. 



The stresses produced by harmonic inequalities of high orders 



are next considered. This is in effect the case of a series of 

 parallel mjuntains and valleys, corrugating a mean level surface 

 with an infinite series of parallel ridges and furrows. 



Numerical calculation shows that if we take a series of moun- 

 tains, whose crests are 4000 meters, or about 13,000 feet above 

 the intermediate valley-bottoms, formed of rock of specific 

 gravity 2'8, then the maximum stress-difference is 2 '6 tons per 

 square inch (aljout the tenacity of cast tin) ; also if the moun- 

 tain chains are 314 miles apart, the maximum stress-difference is 

 reached at 50 nnles below the mean surface. It appears that 

 there is no stress at the surface, but the solution is only approxi- 

 mate, for it does not give the stress actually within the mountain 

 masses, but gives correct results at some three or four miles 

 below the mean surface. 



The cases of the harmonics of the 4th and higher orders are 

 also considered ; and it is shown that, if we suppose them to 

 exist on a sphere of the mean density and dimensions of the 

 earth, and that the height of the elevation at the equator is in 

 each case 1500 meters above the mean level of the sphere, then 

 in each case the maximum stress-difference is about four tons per 

 square inch. This maximum is reached in the case of the 4th 

 harmonic at 1 1 50 miles, and for the 12th at 350 miles, from the 

 earth's surface. 



It is then shown that the great terrestrial inequalities, such as 

 Africa, the Atlantic Ocean, and America, are represented by an 

 harmonic of the 4th order ; and that, having regard to the mean 

 density of the earth being about twice that of sujierficial rocks, 

 the height of the elevation is to be taken as about 1500 meters. 



Four tons per square inch is the crushing stress-difference of 

 average granite. From these results it may be concluded that 

 either the materials of the earth have about the strength of 

 granite at 1000 miles from the surface, or they have a much 

 greater strength nearer to the surface. 



This investigation must be regarded as confirmatory of Sir 

 William Thomson's view, that the earth is solid nearly through- 

 out its whole mass. According to this view the lava which 

 issues from volcanoes arises from the melting of solid rock, 

 which exists at high temperature at points where the pressure is 

 diminished, or else from comparatively small vesicles of rock in 

 a molten conditi in. 



Zoological Society, June 2i.— Prof. W. H. Flower, F.R.S. , 

 president, in the chair. — The Secretary read a report on the 

 additions that had been made to the Society's Menagerie during 

 the month of May, 18S1, amongst which special attention was 

 called to an African Wild Ass (Equus laniof^ui) from Upper 

 Nubia, and a White-marked Duck (Anas specularis) from Ant- 

 arctic America, both new to the collection. — Mr. U. Bowdler 

 Sharpe exhibited a specimen of Podilymbus podiceps, stated to 

 have been killed at Kadipole, near Weymouth, in the winter of 

 1880-81. — Mr. W. A. Forbes read a paper on the Petrel called 

 Thallasiidroma nereis, by Gould. This, he showed, was not a 

 true Proccllaria, but must form the type of a new genus, to be 

 called GarroJia, most closely allied to Oceanites, Fregetta, and 

 Pclagodroma, and constituting with them a distinct family of 

 "Tnbinares," proposed to be called " Oceanitidse." — Mr. W. 

 A. Forbes read a paper on the conformation of the thoracic 

 extremity of the trachea in the " Ratite" birds, noting specially 

 a highly-developed syrinx in the genus Rhea, in n hich respect it 

 differed from all the other genera comprised in that group. — A 

 communication was read from Mr. George F. Bennett, C.M.Z.S., 

 containing an account from personal ob-ervation of the habits of 

 the Echidna hystrix of Australia. — Mr. G. A. Boulenger read a 

 paper on the Lizards of the genera Lacerta and Acanthodaciylus, 

 prepared after a study of specimens in the British Museum. — 

 Mr. F. C. Selous read a paper on the Antelopes that had come 

 under his observation in Central South Africa. He exhibited a 

 series of skins of the Bush- Buck {Tragelaphus sylvaticus), and 

 pointed out their variations indifferent locallities ; also specimens 

 of the Poku (Cobtis vardoni), and the Speke's Antelope (Tra- 

 gelaphus Spikii). — A communication was read from the Rev. O. 

 P. Cambridge, describing some new genera and species of 

 Araneidea. — Mr. Sclater pointed out the generic divisions of 

 the Bucconida: which he proposed to adopt in his monograph of 

 the group now approaching completion, and charac'erised a new 

 species of the family under the name Ncnnula cineracea. — Mr. 

 R. Bowdler Sharpe communicated some notes on new or rare 

 species of flycatchers lately added to the British Museum, 

 principally from the Gould collection, and which it was proposed 

 to call Malnrtis cyanochlamys, Siphia ohscura, and Rhipidura 

 MacgUlivrayi. — A second paper by Mr. Sharpe contained an 

 account of several collections of bu'ds formed by Mr. W. B. 



