. October 6, 1910] 



NATURE 



443 



Laurentian gneisses, and contrasted the slight meta- 

 morphism of the Lower Huronian conglomerates of 

 Cobalt with their alteration into gneiss at Michipicoten 

 by infolding with Keewatin batholites. 



Dr. Lane stated the three possible sources of the 

 gneissic rocks known as the Laurentian, and from a com- 

 parison of the size of their constituents with those of the 

 adjacent rocks concluded that the Laurentians must be 

 due to the ascent of deep-seated fluid material. 



In the afternoon meeting various subdivisions of the 

 pre-Cambrian rocks were advocated. Mr. W. G. Miller 

 explained the classification used by the Geological Survey 

 of Ontario, which adopts three main divisions : the 

 Keweenawan for the upper sandstones, the Huronian for 

 the underlying schists, quartzites, &c., and the Laurentian- 

 Keewatin for the basal comple.x. Prof. Coleman objected 

 !o the retention of Laurentian except as a temporary 

 ;onvenience, since the Laurentian are intrusive rocks of 

 various ages. Dr. Sederholm explained the classification 

 he had adopted for Finland and Scandinavia, where the 

 pre-Cambrian system is broken up by great unconformities 

 into divisions, each of which he thought from its thick- 

 ness must correspond to the groups, and not to the 

 systems, of the post-Cambrian rocks. He objected to the 

 ^erms previously used, and proposed to call the pre- 

 Cambrian rocks the Progonozoic, and to divide them into 

 three divisions, the Archeo-, Meso-, and Naeo-progonozoic. 



Another case of supposed PaIa;ozoic schists proving to 

 be pre-Cambrian was described by Prof. J. F. Kemp 

 from evidence displayed during recent work for the New 

 York water supply. 



President van Hise supported the threefold division of 

 the pre-Cambrians, and Mr. Fermor the twofold division 

 found more convenient in India, and referred to Sir 

 Thomas Holland's term Purana for the non-foliated pre- 

 Cambrian sediments. Miss Raisin directed attention to 

 the analogous case in the English Midlands, and to Lap- 

 worth's term Uriconian for the comparatively unaltered 

 pre-Cambrian volcanic series. 



The petrographic section, under the presidency of Dr. 

 Teall, devoted a morning to discussion of the principles of 

 rock classification. Prof. Adams exhibited photographs of 

 t.he structures he had produced in rocks, including the 

 formation of flaser gabbro or augen gneiss by pressure at 

 temperatures of 450° F. No fresh minerals were produced, 

 but by mechanical movements the material of a massive 

 diabase was rearranged as a gneiss. 



Prof. Vogt urged the claim of eutectics as a factor in 

 rock classification. Dr. A. L. Day explained the aims 

 and methods of the researches on mineral formation and 

 stability conducted in the Carnegie Institute, and expressed 

 confidence that their methods could in time be applied to 

 oven such complex mixtures as ordinary rocks. 



Dr. Whitman Cross defended the quantitative system of 

 rock classification from recent criticisms, and said that 

 the other systems were only less arbitrary in the degree 

 that they were less definite. He referred to Becke's petro- 

 graphic types — the -Atlantic and Pacific — as based on dis- 

 tinctions that could not be sharply defined. Dr. Evans 

 repeated his criticisms on the quantitative system, and the 

 general discussion was continued by Dr. Benett, Prof. 

 Kcenigsberger, and Prof. Tschirwinsky. 



Meetings of the other sections were devoted to tectonic 

 geology, especially of Switzerland, to the causes of the Ice 

 age, to polar geology, applied geology, stratigraphy, and 

 palaeontology. 



At the final meeting it was decided that the next meet- 

 ing, in 1913, should be in Canada, and the hope expressed 

 that the meeting in igi6 should be in Belgium. 



THE THOMAS YOUNG ORATION. 

 pROF. R. W. WOOD, in delivering the Thomas Young 

 Oration at the Optical Society on Thursday, Sep- 

 tember 29, described some apparatus with which he has 

 been experimenting recently. The first of these, which 

 he calls the echelette grating, is an instrument occupying 

 a position between the echelon and the ordinary diffraction 

 grating. It is a grating ruled with a crystal of carbor- 

 undum on gold deposited on copper ; the carborundum has 

 the advantage over a diamond point of having perfectly 



NO. 2136, VOL. 84] 



straight sides meeting at an angle of 120°. The spacing is 

 about ten times as coarse as usual. No metal is removed 

 in ruling, but the gold is compressed so as to form ridges 

 and hollows. The sides of these ridges are highly polished 

 and almost optically flat. Such a grating may have 

 various faults, such as having a fiat or irregular top to 

 the ridges, or the sides of one groove may be deformed in 

 ruling the next ; tests to determine whether the grating is 

 free from faults were described. 



A variety of gratings is obtained by altering the posi- 

 tion of the crystal in ruling ; thus some gratings have 

 their two sides equally inclined to the surface of the plate, 

 and in others there are inequalities in the inclinations of 

 various magnitudes. The gratings thus obtained, with a 

 known form of groove, have been used to determine the 

 causes which throw the greater part of the light of a 

 definite wave-length into one particular spectrum. These 

 gratings bear the same relation to heat waves that the 

 ordinary diffraction grating bears to light waves ; thus 

 they are specially suitable for use in investigations into 

 radiant energy, being many times more efficient than 

 prisms of rock salt. Diagrams were shown which demon- 

 strated the greater resolving power of the grating com- 

 pared with the rock-salt prism. A number of gratings 

 were exhibited, and some of the tests for detecting faults 

 were shown. A demonstration was also given of the 

 ability of these gratings to concentrate the light of a 

 definite colour into a particular spectrum. 



Prof. Wood next described his mercury telescope, in 

 which the mirror is a vessel containing mercury, the 

 surface of which is made to assume a steady parabolic 

 form by rotation under gravity. The practical difficulties 

 to be overcome in preventing ripples on the mercury 

 surface due to vibration or to a very slight obliquity in 

 the axis of rotation were described. The mercury vessel 

 is mounted on an axis with two conical bearings, and the 

 whole mount is placed on a stand with levelling screws. 

 To avoid the excessive friction due to conical bearings, the 

 greater part of the weight is taken by a steel ball under 

 the centre of the objective. A magnetic drive was first 

 attempted, but was abandoned in favour of a mechanical 

 connection consisting of half a dozen fine threads of pure 

 elastic, thus any vibrations in the motor are absorbed by 

 the elastic threads. Some star trails taken with the 

 instrument in and out of adjustment were described. 



Finally, some photographs of landscapes taken with 

 infra-red light were shown. 



THE POLAR ESKIMOS^ 

 A NTHROPOLOGISTS are now beginning to realise 

 •^ the necessity of supplementing the methods of a 

 general ethnographic survey by a more intensive study of 

 smaller groups within limited areas. A good example of 

 this class of investigation is provided by the account of 

 the Polar Eskimos by Dr. H. P. Steensby, who was a 

 member of the expedition commissioned by the Danisb 

 Missionary Society in 1909 to establish a station in 

 Greenland. 



The tribe known as the Polar Eskimos occupies the 

 west side of the Hayes Peninsula, extending from north- 

 west Greenland towards the west between the Kane Basin 

 in the north and the Melville Sound in the south. At 

 present they number about two hundred souls. Compared' 

 with the people of the more southerly west Greenland,, 

 they appear to be a different race, the Mongolian type 

 prominent in the latter region being here replaced by 

 that called by Dr. Steensby the Indian. The so-called' 

 Mongolian racial characters, the low nose, oblique eyes, 

 fiat face, broad and large cheek-bones, are more prominent 

 in the women than in the men. The skull is of the 

 dolichocephalic class. The skin has always a yellowish- 

 ground-colour, and the so-called " Mongolian spot " is 

 present* in the sacro-lumbar region of children. 



Much of the existing culture of the tribe seems to be 

 due to the emigration of a body of their kinsmen from 

 the coasts of North Devon and Ellesmere Land in the 

 early 'sixties, and they present the almost unique condi- 

 1 " Contributions to the Ethnology and Anthropogeocjraphy of the Polar 

 Eskimos." By Dr. H. P. Steensby. Pp. 253 — 406. (Copenhagen : Bianco- 

 Luno, 1910.) 



