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NA TURE 



[December 30, 1922 



around the relict-covered bed of the ancient lake 

 Cahuilla -- i.e. the Colorado Desert in the exact 

 original sense of this term. The enormous numbers 

 of shells present in many parts of the valley and 

 the discovery of many of the same species still 

 flourishing in certain of the outlying springs and 

 rivulets have long ago attracted attention to this 

 section of the fauna. A list of papers on the mollusca 

 of the Colorado Desert is given. 



Animal Associations of some Crustacea. — A 

 memoir on the Pontoniinae — a sub-family of the 

 decapod Crustacea — based chiefly on material in 

 the collection of the Zoological Survey of India, is 

 contributed by Dr. Stanley Kemp to the Records 

 of the Indian Museum (xxiv. 1922, pp. 113-288, 

 9 pis.). A detailed systematic account of and keys 

 to the genera and species are given, and Dr. Kemp 

 directs attention to the ability shown by members 

 of the sub-family to form associations with other 

 animals. Some are found on sponges, others on 

 actinians, on Alcyonaria, or on corals, a few on star- 

 fishes and sea-urchins, many live on crinoids, a 

 considerable number of species live in the mantle 

 cavity of bivalve molluscs, and some are known from 

 the branchial sac of ascidians. In the case of those 

 which live in the mantle cavity of bivalve molluscs, 

 in practically every example a male and female 

 prawn are found together in the same mollusc, and 

 Dr. Kemp infers that after the prawns are once estab- 

 lished in their host they never leave it. A list of the 

 animal associations recorded in the Pontoniinae is given. 



American Oligocene Mammals. — Mr. W. J. 

 Sinclair has two papers on American fossil vertebrates 

 in a recent number of the Proceedings of the American 

 Philosophical Society (vol. lxi. 1922, with text figs.). 

 The first, treating of 'The Small Entelodonts of "the 

 White River Oligocene," discusses the relationships 

 of Archaotherium coarctatum, Cope, and A. mortoni, 

 Leidy, in the light of fresh specimens acquired by 

 one of the Princeton Expeditions. After a careful 

 analysis it is suggested that, so far as the assumed 

 primitiveness of A. coarctatum is concerned, every 

 one of its characters which might be regarded as 

 primitive is possessed in some degree by specimens 

 which differ from it in other respects, so that it would 

 be necessary either to name every variant or to refer all 

 to one species for which the name A . mortoni would 

 have priority. The other paper, on " Hvdracodons 

 from the Big Badlands of South Dakota," dis- 

 tinguishes four specific types : — H. arcidens, Cope, 

 H. nebrascensis, Leidy, H. apertus, sp.n., and H. 

 leidyanus, Troxell ; and their range in time is shown 

 in tabular form. The distinctions between these 

 species, or possibly subspecies, are based primarily 

 upon structural differences in the upper posterior pre- 

 molars. No intermediate stages have been observed. 



The Lavas of Snowdonia. — A marked gap in 

 our detailed knowledge of the igneous rocks of the 

 Snowdon area has been filled by Howell Williams 

 in a recent paper in the Proceedings of the Liverpool 

 Geological Society (vol. 13, part 3, p. 166, 1922). 

 The author deals with the country near and mainly 

 east of Capel Curig, tracing the devitrified rhyolitic 

 lava-flows of Snowdon across the district. Con- 

 siderable attention is given to alterations due to 

 solfataric action, and the puzzling " bird's-eye 

 slates," with their strings of small ellipsoids of 

 calcite arranged across their bedding, are compared 

 with those of the Lake District, and are attributed 

 to an epoch when carbon dioxide was the principal 

 escaping gas. These unusual rocks are limited to 

 an horizon between the middle and uppermost 

 rhyolites of the Capel Curig suite. 



NO. 2774, VOL. I io] 



Earth Currents in France. — In La Nature 

 (November 25, p. 339, and December 2, p. 355) Dr. 

 Albert Nodon has described a new series of researches 

 upon the electric currents flowing in the earth. 

 An observing station for this- purpose was set up 

 in the summer of 1921 near Sauveterre in the Basses 

 Pyrenees ; the district is far removed from any 

 industrial electric circuits, being in a wide, well- 

 watered prairie on clay soil, the humidity of which 

 is probably fairly constant ; it is therefore well 

 suited in many important respects for such observa- 

 tions. Four overhead wires (the lengths of which 

 are not stated) branch out in directions north-south, 

 east-west, south-east to north-west, and south-west 

 to north-east, from a small observatory. The earth- 

 contacts at the ends of the wires were made by large 

 zinc plates ; the contact electro-motive forces from 

 these plates annul one another and appear to have 

 given no trouble. The currents were measured by 

 a milliamperemeter, eye-readings being taken with 

 a lamp and scale ; no continuous photographic 

 registration is arranged. The conductivity of the 

 soil in various directions is measured from time to 

 time by applying a known E.M.F. to the wires. 

 Other observations include the earth's horizontal 

 magnetic force, and the intensity of penetrating 

 radiation, the latter being measured by a delicate 

 electrometer in a closed metal case. The currents 

 which flow along the direction of latitude appear 

 to be small and invariable in direction, namely, 

 from east to west ; those from north to south are 

 very variable both in direction and magnitude ; 

 the currents in the intermediate directions agree 

 with the resultant of the east-west and north-south 

 currents along these directions. The conductivity 

 of the soil appears to vary in parallel with the 

 intensity of penetrating radiation, and also to be 

 augmented when the earth currents are large. 

 Various other correlations, with meteorological and 

 solar phenomena, are indicated, but the results can 

 only be regarded as provisional in view of the short 

 period over which the observations extend. 



Street Lighting. — A meeting of the Illuminating 

 Engineering Society, on December 12, was devoted 

 to a discussion on street-lighting. Mr. Haydn T. 

 Harrison, in an introductory paper, pointed out the 

 importance of correct distribution of light and 

 described several devices for improving the natural 

 distribution of illuminants, notably the holophane 

 lantern and the " longitudinal system " for which 

 he himself -was responsible. He pointed out that 

 the classification of streets in terms of minimum 

 illumination adopted in the United States agreed 

 closely with that recommended in this country, 

 and urged that " minimum horizontal illumination " 

 was the best basis of specification for public lighting. 

 A contribution by Mr. L. Gaster dealt mainly with 

 street lighting in relation to traffic, and some "figures 

 were quoted showing how the diminished lighting 

 in war time had contributed to the increase in street 

 accidents. Experiments in 32 American cities in- 

 dicated that 17-6 per cent, of accidents occurring 

 at night were due to inadequate illumination. Dr. 

 Clayton Sharp gave an interesting survey of methods 

 adopted in American cities. A feature of such 

 tests has been the utilisation of a length of road for 

 actual experiments with different forms of lamps. 

 Another point, mentioned by Mr. Thomson, chairman 

 of the Street Lighting Committee of the Westminster 

 City Council, is the desirability of arranging lights 

 so as to illuminate the exteriors of important build- 

 ings, so as to render them visible by night as well 

 as by day. The advice of architects in considering 

 this aspect of public lighting would be of value. 



