April i, 1909] 



NA TURE 



147 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, January 14. — "On ihe Depression of the 

 Filament of Maximum Velocity in a Stream flowing 

 through an Open Channel." By A. H. Gibson. Com- 

 municated by Prof. J. E. Petavel, F.R.S. 



In a stream flowing through an open channel the fila- 

 ment of maximum velocity is not, as might be expected, 

 in the surface and in the centre of the stream, but is 

 usually at some distance below the surface. No satis- 

 factory explanation of the reason for this has hitherto been 

 given. In this paper the phenomenon is attributed to the 

 effect of transverse currents which sweep up each side of 

 the stream, along the surface towards the centre, down 

 near the centre, and outwards near the bottom. These 

 currents, the existence of which may be foretold from 

 theoretical considerations, and which have been observed 

 by the author in a number of streams and open channels, 

 spread a layer of slowly moving water over the surface of 

 the stream, and so depress the filament of maximum 

 velocity. 



This explanation also accounts for several subsidiary 

 phenomena which are observed in river gauging, such as 

 the effect of the roughness of the sides and of the bottom, 

 and of the ratio of breadth to depth on the depth of this 

 filament. 



January 21. — " The Leakage of Helium from Radio- 

 active Minerals." By the Hon. R. J. Strutt, F.R.S. 



In a paper published in Roy. Soc. Proc, A, vol. l.x.x.\i. 

 (1908), p. 272, the author showed that phosphatised bones 

 and similar materials were notably radio-active, and that 

 helium could be detected in them. The quantity of helium 

 found was not, however, uniformly greater in the geo- 

 logically older materials than in younger ones of equal 

 activity. This was hypothetically attributed to escape of 

 helium in certain cases. The author desired, if possible, 

 to observe directly the escape of helium from radio-active 

 minerals at the ordinary temperature. 



It was found that after a radio-active mineral had been 

 powdered, helium was evolved from it, rapidly at first, 

 then at a diminishing rate. The following observations 

 illustrate this. 



A quantity (337 grams) of monazite from the Transvaal 

 was powdered and passed through a wire gauze sieve of 

 120 threads to the inch. This took about one hour. 

 Immediately afterwards it was put in a bottle and the 

 air pumped out. The rate of evolution of helium in cubic 

 millimetres per day per kilo, of material was as follows : — 



Time (day.) 

 0031 



0-59 

 1-6 



2-6 



4-6 

 10-6 

 33-0 



261 

 766 

 17-1 



12-3 



957 

 4-38 

 I-I4 



The whole quantity which has escaped while the mineral 

 has been under observation is but an insignificant fraction 

 (probably less than a 500th ') of the whole quantity present. 



-Moss (Roy. Dub. Soc. Trans., vol. viii., p. 153) has 

 observed that quantities up to i per cent, of the helium 

 contained in a mineral can be liberated by grinding in a 

 vacuum. The present observations show that this is but 

 the fust rapid stage of a long-continued leakage of helium 

 from the newly created surfaces. The view that heat 

 generated in grinding is the important factor appears un- 

 tenable, for in that case escape of helium should cease on 

 cooling. • 



It was found that pieces from the same stock of 

 monazite, about the size of a lump of sugar, which had 

 not been fractured since they came into the possession of 

 the author two years ago, evolved helium at the rate of 

 0-002 c.mm. per kilo, of material per diem. 



This rate, though quite insignificant in comparison with 

 that exhibited by the powdered material, is much in excess 

 of the probable rate of generation of helium by radio-active 



1 This sample of monazite was very poor in helium, containing only ^\,c.c. 

 per gramme. 



NO. 2057, VOL. 80] 



change. It follows that the present stores of helium could 

 never have been accumulated had the present rate of 

 evolution prevailed throughout the life-history of the 

 mineral. 



With the view of testing a mineral more nearly in its 

 natural condition, experiments were made on thorianite, 

 which occurs in gravels, in detached cubic crystals, washed 

 out of their original matrix. This, too, showed a con- 

 siderable leakage of helium (0069 c.mm. per kilo, per 

 diem). 



Under laboratory conditions the rate of escape of helium 

 from minerals always far exceeds the rate of production 

 by radio-active change. Therefore the conditions under 

 which the life of the minerals has been mainly passed, deep 

 down in the earth, where atmospheric agencies have no 

 place, must be supposed more favourable to retention of 

 helium, for otherwise the present accumulation could never 

 have been formed. The observations here recorded leave 

 little room for surprise that fossilised bones and other 

 materials do not always contain as much helium as would 

 be expected from their radio-activity and geological age. 



Geological Society, March lo. — Prof. W. J. SoUas, 

 F.R.S., president, in the chair. — Some notes on the 

 neighbourhood of the Victoria Falls (Rhodesia) : _T. 

 Codrington. An account is given of the way in which 

 the basalt lies in the valley of the Zambezi below and 

 above the Victoria Falls, and how this determines the 

 features of the river is pointed out. The basalt through 

 which the Batoka Gorge has been cut appears in the 

 course of the Zambezi for two miles above the Victoria 

 Falls, causing rapids. It then disappears, and the river 

 above flows quietly between alluvial flats for five miles, the 

 basalt being traceable here and there below the water 

 until above Candahar Island it again rises and constittites 

 the bed of the river from bank to bank, causing rapids. 

 The discovery of stone implements and artificially worked 

 stones in the gravel and the bed of the Maramba is noted. 

 The majority of flakes and flaked stones having no trace 

 of design over those that can be considered as implements 

 suggests that the manufacture of stone tools on a large 

 scale was here carried on for use in the sand-covered 

 country on both sides of the Zambezi, where there is no 

 stone. There appears to be no evidence as to the age of 

 the implements found near the Zambezi. — A contribution 

 to the petrography of the New Red Sandstone in the west 

 of England : H. H. Thomas. The paper is supplementary 

 to one dealing with the mineralogical composition of the 

 pebble-bed. A list of minerals identified, and tables show- 

 ing their distribution, are given. It is suggested that 

 anatase occurs both as detrital crystals and as_ crystalline 

 groups formed in the rocks since their deposition. The 

 forms presented by grains of staurolite, as well as certain 

 crystals of tourmaline with an unusual habit, are described. 

 It' is recognised that the divisions of the New Red Sand- 

 stone, although linked together by a similarity of minera- 

 logical composition, present differences indicative of varia- 

 tions in the source of supply and conditions of deposition. 

 With regard to the vertical and horizontal distribution of 

 minerals, staurolite is abundant in the Lower Breccias and 

 Sandstones of the extreme south of Devon, but less plentiful 

 northwards ; garnet is present in all the New Red rocks 

 of North Devon and Somerset, but in south and central 

 Devon only occurs in the Lower Marls and in the Upper 

 Marls and Sandstones. 



Physical Society, March 12. — D-. C. Chree, 



F.R.S., president, in the chair.— The effect, of radiations 

 on the brush discharge : A. E. Garrett. Willows and 

 Peck in 1905 found that radium radiations can extinguish 

 a brush discharge produced by a Wimshurst machine when 

 the gap is greater than 3-4 cm. These experiments show 

 that the phenomena can be produced by an induction coil 

 giving a 6-inch spark. The observation that the rays 

 are responsible for the effects produced is confirmed. The 

 effect of the nature of the anode on the sensitivity of the 

 positive brush is dealt with. It has been found that the 

 sensitive nature of the brush depends upon the oscillatory 

 nature of the discharge, and probably a side discharge 

 takes place when the brush is extinguished by the radium. 

 — Pirani's method of measuring the self-inductance of a 



