October 2, 1919] 



NATURE 



107 



be most probably successful. They should be supple- 

 mented by laboratory studies of the relations of such 

 subsidiary crystallographic characters to the environ- 

 ment in the case of crystals which can be formed 

 under normal conditions of temperature and pressure, 

 arid therefore under the immediate observation of 

 the experimenter. Some work has, in fact, already 

 been done on the effects on these characters of the 

 presence of other substances in the same solution. 



In the study of the secondary alterations of metal- 

 liferous deposits, especially those which consist of the 

 enrichment of mineral veins by the action of cir- 

 culating solutions, either of atmospheric or intra- 

 telluric origin, the study of pseudo-morphs gives, of 

 course, valuable assistance in determining the nature 

 of the chemical and physical changes that have taken 

 place. 



The problem of the structure and nature of the 

 earth's interior, inaccessible to us even by boring, 

 would seem at first sight to be well-nigh insoluble, 

 except so far as we can deduce from the dips and 

 relations of the rocks at the surface their downward 

 extension to considerable depths. We can, however, 

 gain important information about the physical condi- 

 tion of the deeper portions from the reaction of the 

 earth to the external forces to which it is subjected, 

 and still more from a study of the " preliminarv " 

 earthquake tremors that traverse it, the time occupied 

 in their passage, and the difference in intensity of 

 those that follow different paths. These methods are, 

 however, not applicable to the earth's crust. Its 

 physical characters appear to be distinct from those 

 of the interior, but very little is as yet definitely 

 known about them, except, of course, in the neigh- 

 bourhood of the surface, and for this reason thev are 

 usually ignored in calculating the paths of tremors 

 traversing the earth. It seems to be separated from 

 the deeper portions of the earth by a surface of dis- 

 continuity ;it which earthquake vibrations travelling 

 upwards towards the surface may be reflected. Cal- 

 culations based on the total time taken by these 

 reflected waves to reach the surface after a second 

 passage through the earth's interior appear to indi- 

 cate that this surface of discontinuitv, whatever its 

 nature may be, is at a depth of about twentv miles, 

 though there can be little doubt that this depth varies 

 considerably from point to point. 



There must be numerous surfaces of discontinuity 

 in the earth's crust in addition to that forming its 

 lower limit. Such would be the boundaries between 

 great tracts of granite or granitoid gneiss and the 

 basic rocks that in all probability everywhere underlie 

 them ; the surface dividing gneisses and crystalline 

 schists from unmetamorphosed sediments overhing 

 them unconformably ; that between hard Palajozoic 

 rocks and softer strata of later age ; and the surfaces 

 of massive limestones or sills. 



It deserves consideration as to how far it mav be 

 possible to add to our knowledge of the earth's crust 

 by experimental work with a view of the determina- 

 tion of surfaces of discontinuity by their action in 

 reflecting vibrations from artificial explosions, a pro- 

 cedure similar to that by means of which the presence 

 of vessels at a distance can be detected by the reflec- 

 tion of submarine sound-waves. The ordinarv seismo- 

 graphs are not suited for this purpose ; the scale of 

 their record, both of amplitude and of time, is too 

 small for the minute and rapid vibrations which would 

 be expected to reach an instrument situated several 

 miles from i\n explosion, or to distinguish between 

 tlirect vibrations and those that mav arrive a second 

 <ir two later after reflection at a surface of discon- 

 tinuity. .As the cylinder on which the record is made 

 wcHild be only in motion while the experiment was 

 NO. 2605, VOL. 104] 



in progress, there would be no difficulty in arranging 

 for a much more rapid movement. At the same time 

 it would be desirable to dispense with any arrange- 

 ment for damping the swing of the pendulum, which 

 would be unnecessary with small and rapid vibra- 

 tions, and v»-ould tend to suppress them. It is 

 possible that it might be better to employ a seismo- 

 graph which records, like that devised by Galitzin 

 shortly before his death, variations of pressure ex- 

 pressing terrestrial acceleration, instead of one which 

 records directly the movements of the ground. It 

 would, however, probably be found desirable to sub- 

 stitute for the piezo-electric record of pressure 

 employed by Galitzin a record founded on the effect 

 of pressure in varying the resistance in an electric 

 circuit. This is, in fact, the principle of the micro- 

 phone and most modern telephone receivers, but 

 quantitatively they are very untrustworthy. This 

 would not rnatter so much for the present purpose, 

 where the time of transmission is the most important 

 feature in the evidence. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



Cambridge. — Mr. B. M. Jones, Emmanuel College, 

 has been elected to the Francis Mond professorship 

 of Aeronautical Engineering at the University, 

 founded by Mr. Emile Mond in memory of his son, 

 who was killed in the war. This is the first pro- 

 fessorship in aeronautics which has been filled in this 

 countrv. Mr. Jones entered Emmanuel College as 

 an Exhibitioner in 1906. He afterwards became a 

 scholar, and obtained First Class Honours in the 

 Mechanical Sciences Tripos of 1909. From 1910 to 

 1912 he was employed on aeronautical research at 

 the National Phvsical Laboratory, and held a research 

 scholarship from the Imperial College, London. In 

 the capacity of an assistant he continued in this 

 work until Mav. 1913, when he left the National 

 Phvsical Laboratory to take up the design of rigid 

 airship construction and other aeronautical work for 

 the firm of Sir G. vV. .Armstrong, Whitworth, and 

 Co. In September, 1914, Mr. Jones joined the Royal 

 Aircraft Establishment, and remained there, carrying 

 out aeronautical research and experimental work 

 until Mav, 1916. He was then transferred to the 

 Armament Experimental Station, Orford Ness, with 

 the rank of captain, R.F.C., eventuallv rising to the 

 position of Assistant Controller of Experiment and 

 Research with the rank of lieut. -colonel. His chief 

 activities were directed towards aerial gunnery and 

 aerial bombing, and in order to gain first-hand experi- 

 ence of fighting conditions he qualified as a pilot and 

 served with No. 48 Souadron, R.F.C., in France 

 during the earlv months of 1916. On being demobi- 

 lised in March' last, Mr. Jones was elected a junior 

 fellow of Emmanuel College, with the post of director 

 of engineering studies at the college. 



Sheffield.— The council has received with much 

 regret the resignatidn of Prof. J. O. Arnold, dean of 

 the faculty of metallurgy and professor of metallurgy 

 in the University since' i88q. Steps will shortly be 

 taken to appoint a successor. 



Dr. J. G. Stewart has been appointed lecturer in 

 engineering at University College, London. 



A CHAIR of laryngology has recently been established 

 in the I'niversitv of Paris, the first occupant of which 

 is to be Dr. Sebileau. 



The sum of 400,000!. has been bequeathed to the 

 University of Sydney by Sir Samuel McCaughey. 



