730 



NATURE 



[August 5, 1920 



the possibility of forecasting any short-period varia- 

 tions in the rainfall. Inasmuch as we are bound to 

 regard the tropics as the first stage in the translation 

 of solar variation into weather, it seems a pity that 

 the result obtained in what is probably the best known 

 region of the tropics in regard to meteorological 

 statistics should appear so meagre and wanting in 

 definiteness. Similar work in temperate regions may 

 well be discouraged, but there is still an enormous 

 mass of data W. W. B. 



Insects of Arctic Canada, 



THE insects of various orders — as well as a few 

 spiders, mites, and centipedes — collected by 

 members of the recent Canadian Arctic Expedition 

 (1913-18) have been recorded and described in vol. iii. 

 of the Report (Ottawa, 1919-20). The lists contain 

 much information of value to students of zoological 

 geography. Among the Lepidoptera (described by 

 Arthur Gibson) it is interesting to see varieties of 

 such well-known British butterflies as Pieris napi, 

 Papilio machaon, and Vanessa antiopa. Most of the 

 Coleoptera (by J. M. Swaine, H. C. Fall, C. W. 

 Leng, and J. D. Sherman) belong to species alreadv 

 known in North America, and the same remark 

 applies to the bees described by F. W. L. Sladen, 

 who points out that bumble-bees are " particularly well 

 adapted to Arctic conditions," and records the capture 

 of five nearly fCni-fed Bombus larvae on Melville Island 

 (75° N. lat.) on June 21, 1916. The sawflies, described 

 by A. G. MacGillivray, are mostly new species, and, 

 as might have been expected, willow feeders. Among 

 the Diptera (by C. P. Alexander, H. G. Dyar, and 

 J. R. Malloch) there are some interesting details of 

 larvae as well as descriptions and records of flies, 

 which are relatively numerous in species. The occur- 

 rence of larvae of Oedemagena tarandi — the warble- 

 fly of the European Reindeer — in Barren-ground 

 Caribou at Bernard Harbour is noteworthy. Mosquitoes 

 of a couple of species of the genus ^des were 

 observed (and felt) in swarms. As regards wingless 

 parasites, Prof. G. H. F. Nuttall records that head- 

 lice (Pediculus capitis) from the . Copoer Eskimo of 

 Coronation Gulf show no varietal distinction from 

 members of the species found elsewhere. Dr. J. W. 

 Folsom enumerates a dozen species cf springtails 

 (Collembola) ; two onlv of these are new, but his 

 figures of structural details, drawn carefullv from 

 Arctic specimens of common and widespread northern 

 forms, will be welcome to students of this order. 



G. H. C. 



Earthquake Waves and the Elasticity of 

 the Earth. 



T^R. C. G. KNOTT delivered a lecture on " Earth- 

 -*-^ quake Waves and the Elasticity of the Earth " 

 before the Geological Society on June 9. He pointed 

 out that seismograph records of the earth-movements 

 due to distant earthquakes proves that an earthquake 

 is the source of two tvpes of wave-motion which pass 

 through the body of the earth, and a third type which 

 passes round the surface of the earth. Before earth- 

 quake records were obtained, mathematicians had 

 shown that these three types of wave-motion existed 

 in and over a sphere consisting of elastic solid 

 material. Manv volcanic phenomena, however, sug- 

 gest the quite different conception of a molten interior 

 underlying the solid crust. At first statement these 



NO. 2649, VOL. 105] 



views seem to be antagonistic, but there is no difficulty 

 in reconciling them. Whatever be the nature of the 

 material lying immediately below the accessible crust, 

 it must become at a certain depth a highly heated 

 fairly homogeneous substance behaving like an elastic 

 solid, with two kinds of elasticity giving rise to what 

 are called the compressional and distortional waves. 

 The velocities of these waves are markedly different, 

 being at every depth nearly in the ratio of i-8 to i. 

 Both increase steadily within the first thousand miles 

 of descent towards the earth's centre, the compres- 

 sional wave-velocity ranging from 4-5 miles per second 

 at the surface to 8 miles per second at depths of 

 1000 miles and more; the corresponding velocities of 

 the distortional wave are 2-5 and 43 at the surface 

 and at the looo-mile depth respectively. At greater 

 depths these high velocities seem to fall off slightly; 

 but the records fail to give us clear information as to 

 velocities at depths greater than about 2500 miles. 

 Down to this depth the earth behaves towards these 

 waves as a highly elastic solid. The elastic constants, 

 which at first increase with depth more rapidly than 

 the density, become proportional to the density, for 

 the velocity of propagation becomes practically steady. 

 About half-way down, however, the material seems to 

 lose its rigidity (in the elastic sense of the term), and 

 viscosity possibly takes its place, so that the distor- 

 tional wave disappears. In other words, there is a 

 nucleus of about 1600 miles radius which cannot 

 transmit distortional waves. This nucleus is enclosed 

 bv a shell of highly elastic material transmitting both 

 compressional and' distortional waves exactly like an 

 elastic solid. 



University and Educational Intelligence. 



Aberdeen.— Dr. R. D. Lockhart has been appointed 

 a lecturer in anatomy. 



It has been decided to institute a full-time lecture- 

 ship in bacteriology in the department of pathology. 



Birmingham.— It has been decided that the fees 

 payable by new students entering the University next 

 session shall be increased by 25 per cent. The 

 reasons given for the increase are : (i) The great rise 

 in the cost of administration, materials, maintenance, 

 taxation, and the wages of employees; and (2) the 

 necessity for improving the payment of the academic, 

 particularly the non-professorial, staff. 



The Vice-Chancellor (Sir Gilbert Barling), according 

 to the Birmingham Post, states that "it is absolutely 

 necessary to increase the stipends of the staff for two 

 reasons :' the present salaries are quite inadequate 

 to maintain the teachers in a reasonable state of com- 

 fort; and, secondly, because without such increase 

 they will be attracted to other places where stipends 

 are more commensurate with ^their capacity and 

 worth." 



Cambridge.— The Balfour Memorial Fund student- 

 ship will be vacant on October i next. Applications 

 are invited for it. Candidates should apply by, at 

 latest, September 15 to Prof. J. Stanley Gardiner, 

 Zoological Laboratory, Cambridge. 



On July 29 the honorary degree of Doctor of Law 

 was conferred upon Dr. A. L. Lowell, president of 

 Harvard University; Prof. J. J. Abel, professor of 

 pharmacology, Johns Hopkins University; and Prof. 

 H. Gushing.' professor of surgery at Harvard Uni- 

 versity. 



Oxford. — The fear expressed in some quarters that 

 the apolication bv the University for a Government 

 grant would check the liberality of private benefactors 

 has proved to be groundless' in at least one con- 



