886 



NATURE 



[December 15, 1923 



Cartinlly defoliated but not killed gradually recover, 

 ut a fresh lot of casii;ilf i<-s o< i ms ;il)()iit four or five 

 years after the disai m. These 



trees, which appc.ti I ucir normal 



amount of foh.i illy died Huddcnly during hot 



weather, and tin -i the crown died at alnnit the 



same time. lix.uuuiation of a large numlxr of dead 

 and dying trees failed to disclose any sufficient para- 

 sitic cause for the casualties. During and immedi- 

 ately after a budworm attack the breadth of the 

 annual rings is very greatly reduced, and a few years 

 after the epidemic the total thickness of the last five 

 years' rings might be reduced to a quarter of the 

 normal for the prc-budworm period. At the same 

 time the leaf area of the trees has been increasing very 

 rapidly. Thus a time is reached when, during hot, 

 dry weather in July, the water-conducting tissue is 

 insufl'jcient to meet the needs of the transpiring leaves 

 and the crown dies from lack of water. Thus death 

 may be due to a lack of co-ordination between shoot 

 growth and cambial activity. 



Zoological Society, November 20. — Dr. A. Smith 

 Woodward, vice-president, in the chair. — W. E. Le Gros 

 Clark: Notes on the living tarsier ( Tarsitts spectrum). — 

 Sir Sidney F. Harmer : Cervical vertebrae of a gigantic 

 blue whale from Paniima. — J. R. Garrood : Two 

 skeletons of the cetacean Pseudorca crassidens from 

 Thomey Fen, Cambridge. — Dr. Francis, Baron 

 Nopsca : Reversible and irreversible evolution ; a 

 study based on reptiles. — C. Crossland : Polychaeta of 

 tropical East Africa, the Red Sea, and Cape Verde 

 Islands ; and of the Maldive Archipelago. — Miss Joan 

 B. Procter : (i) On new and rare reptiles from South 

 America, (2) On new and rare reptiles and batrachians 

 from the Australian region. 



Geological Society, November 21. — Prof. A. C. 

 Seward, president, in the chair. — L. J. Wills : The 

 development of the Severn Valley in the neighbour- 

 hood of Iron-Bridge and Bridgnorth ; with a section 

 on the Upper Worfe Valley, in collaboration with 

 E. E. L. Dixon. The area investigated is roughly 

 delimited by the following localities : Much Wenlock, 

 Buildwas, Oakengates, Shifnal, Worfield, Hampton 

 Loade, Morville. Detailed mapping of the drifts has 

 shown, first, that the Buildwas area was as deeply 

 eroded as now in pre-Glacial times ; and, secondly, 

 that a belief in the existence of the Iron-Bridge 

 Gorge at that time is incompatible with the distribu- 

 tion of the drifts on the plateau above Iron-Bridge, 

 and with the features of the gorge. The. gorge is of 

 late-Glacial origin, and the Worfe Vale was formerly 

 the main drainage-line on the south-east side of the 

 plateau. Practically the whole district was under 

 ice at the maximum of the north-western or Irish-Sea 

 glaciation. Wlien retreat began, the ice-sheet 

 separated into two lobes that remained confluent in 

 the north. The waters of the Glacial lakes formed 

 west and north of the watershed escaped at different 

 times over different cols. One of these overflows is 

 of especial importance in connexion with the origin 

 of the Iron-Bridge Gorge : namely, the Lightmoor 

 overflow, about a mile north of Iron-Bridge. Up 

 to about this stage, the Worfe and its tributaries 

 (one of which now became the Iron-Bridge Gorge) 

 had been engaged in clearing the drift out of their 

 valleys, and in reducing the thalweg of the trunk 

 river to a base-level. Hereafter deposition of the 

 '' Main " Terrace of the Severn and of the terrace- 

 like gravels of the Worfe commenced. Long after 

 the initiation ot tlu- Iron-Bridge Gorge, ice still 

 covered the upper \\ Orfe \'alley. When the ice 

 retired to the nortli of the watershed hereabouts. 

 Glacial Lake Newport came into being, and subse- 

 quently united with the Build wa-^ lake on the 



NO. 2824, VOL. I 12] 



retreat of the ice-front from the foot of the Wrekr 

 The outflow at Iron-Bridge thus increased. I! 

 subsequent rejuvenation of the Severn below In^: 

 Bridge was probably brought about chiefly by an 

 elevation of tne whole land relative to the sea. Stages- 

 in this rejuvenation are marked by terraces. 



Royal Microscopical Society, Xoveml>er 21. — Prof. 

 F. J. Cheshire, president, in the chair. — F. I, G. 

 Rawlins : The miscroscope in physics. A strong 

 plea is made for the closer union of phvsirs AtA 

 microscopy, more especially for the un' of 



work in physical optics by the amateur n iist. 



Assuming the availability of an instrument li'ttcd 

 with Nicols, a convergent substage systrm and a 

 Beckd lens above the eyepiece, observat' be 



made of the traces of the family of 1 itic 



surfaces, each with its characteristic rctarduiion. 

 The work can be made quantitative by employing 

 monochromatic light. If the usual means of obtain- 

 ing such radiation are not at hand. Wratten filters 

 (especially Naphthol Green) are efficient, though their 

 range of usefulness is limited. The number of 



fringes observed with objectives of diff^rer --cal 



aperture can be represented by an • lal 



expression of the form F=Fq«-*'*, whcic . .. the 

 equivalent focal length of the objective and N the 

 number of fringes observed (see R.-iwliim Phil 

 Mag. xliii. p. 766, and xlvi. p. 992). 



Edinburgh. 



Royal Society, November 5. — T. J. Jehu and R. M. 

 • Craig : Geology of the Barra Isles. The rocks are- 

 mostly members of the Archaean complex, and these 

 are of igneous origin, the prevalent types being 

 biotite and hornblende gneisses. Muscovite is also 

 present in the more acid types, and locally some of 

 the gneisses are rich in garnets. The foliation planes- 

 usually strike N.N.W. and S.S.E., with a dip to 

 the E.N.E. at varying angles. Intrusions into the 

 orthogneisses occur in the form of ^ranulites and 

 pegmatites. The Archaean complex is affected by 

 well-marked zones of shearing, along which mylonisa- 

 tion and the production of flinty crush phenomena- 

 can be traced. The macroscopic and microscopic 

 characters and behaviour of the flinty crush material 

 prove that these p>eculiar rocks are the product of 

 mechanical stresses which at places have raised the 

 temperature to an extent sufficient to bring about 

 partial fusion of the crushed members of the complex, 

 followed in certain cases by incipient crj'stallisation. 

 The later dj'kes include olivine dolerites, crinanites. 

 quartz dolerites, and camptonites. EWdences of 

 glaciation are conspicuous, and prove that the ice 

 moved over the islands from S.E. to N,W. — T. H. 

 Osgood : Variation in photo-electric activity with 

 wave-length for certain metals in air. As a source 

 of ultra-violet hght, a quartz mercury-vapour lamp 

 was used in connexion with a monochromatic 

 illuminator. The metal plates were tested in air at 

 atmospheric pressure, due attention .being paid to 

 the " fatigue " which is known to take place under 

 these conditions. The results are of interest and ' 

 may be of some practical importance in connexion 

 with the physiological effect of ultra-violet light. 

 As the primary cause of the physiological chanc 

 produced by hght is probably photo-electric actif 

 the photo-electric activity of a metal plate nid . 

 serve as a means of estimating the quaht>' and 

 intensity of the effective radiation. — H. W. TurnbuII : 

 A geometrical interpretation of the complete systeni 

 of the double binar\'^ (2, 2) form. The double binary 

 form may undergo an algebraic transformation wliich 

 corresjxjnds to a generalised geometrical inversion. 

 Here the con variants of a (2, 2) form reveal sets of 



