February ii, 1909] 



NA TURE 



447 



SOCIETIES AND ACADEMIES. 

 London. 



Royal Society, Dcceiiiljcr lo, 190S. — "Potential tiradient in 

 (jIow Uiscliarges (roni a Point to a Plane." By J. VV. 

 Bispham. Communicated by Sir J. J. Thomson, F.R.S. 



Tlirue types ol discharge were examined ; for very small 

 currents (type A) the glow was limited to the immediate 

 neighbourhood of the point. For larger currents (.type B) 

 the luminous glow spread out in a conical form from point 

 to plate, and the current, as indicated by a telephone in 

 circuit, became intermittent. The oscillations ot current 

 amplitude could be augmented and decreased in frequency 

 by capacity and inductance, and striae then began to appear. 

 The striae were absolutely steady to the eye, in spite of the 

 intermittent nature of the current. When the current was 

 still further increased the flow became continuous, and the 

 glow (type C) was limited to the neighbourhood of the axis 

 of discharge. In this condition the point appeared to be 

 exerting no peculiar effect — the discharge was simply that 

 between two small electrodes. 



An e-Nploring electrode was inserted between the point 

 and the plane, and by means of flotation on mercury it 

 could be made to take up any position on the axis relative 

 10 the point and plane. The electrode took up the potential 

 of the gas, and in this way potential curves were obtained 

 and thfc electric force at various points calculated from 

 ihem. 



Electric-force curves were obtained for the A type which 

 indicated that it only possessed a limited range of stability, 

 not being obtained at all for pressures less than 11-3 mm. 

 (point negative) and 3 mm. (point positive) in discharges 

 in hydrogen. Current increase led to the production of the 

 B type of discharge. For the B type of discharge it was 

 observed that the kathode dark space was abnormally 

 large, and also that the kathode glow was a doublet con- 

 sisting of two bright layers separated by a layer of very 

 low luminosity. 



Apparent reversals of field were observed near the elec- 

 trodes, but it was found that these apparent reversals 

 varied with the capacity of the electroscope used to measure 

 the potential, and they were interpreted to indicate local 

 excesses of positive and negative electrification rather than 

 reversals of field. The distortion of the potential curve 

 was increased by increasing the capacity of the electro- 

 scope. No distortion was observed in the case of the C 

 type of discharge, and the capacity of the electroscope did 

 not .affect the readings. Evidently the distortion of the 

 curve was to be associated with the intermittent character 

 of the discharge in type B. 



It was concluded (for type B) that the Crookes dark 

 space w'as positively electrilied, while negative ions were in 

 excess at a point further away from the kathode. Similarly, 

 when striae were obtained the anode side of a stria was 

 positively electrified, while the kathode side was negatively 

 electrified, as indicated by the potential curves. In the 

 C type of discharge a constant and normal kathode fall 

 was obtained for wide ranges of pressure and current 

 variation, and the curves were of the same type as has 

 been obtained by Prof. H. A. Wilson for discharges 

 between small plane electrodes. They afforded testimony 

 as to the efficient working of the explorer. In this type 

 of discharge, also, the kathode dark space was observed 

 to be unusually large, and the negative glow resembled 

 rather a large stria embedded in a pale blue halo. Some 

 of the curves obtained for the point glow (.\ type of 

 discharge) indicated that the discharge proceeded in two 

 stages, a discharge from the point to the neighbouring 

 gas, succeeded by a discharge from this gas to the plate. 



Royal Microscopical Society, January 20.— Anniversary 

 meeting. — Lord .Avebury. F.R.S., president, in the chair. 

 — Presidential address, entitled " On Seeds, with Special 

 Reference to British Plants " : Lord Avebury. In this 

 the president more particularly dealt with the seeds of 

 gymnosperms and monocotyledons, in continuation of the 

 address of the previous year, in which the seeds of dicoty- 

 ledons wore considered. 



Physical Society. January 22.— Dr. C. Chree, F.R.S., 

 president, in the chair. — Effective resistance and inductance 

 of a concentric main, and methods of computing the Ber 

 and Bei and allied functions : Dr. \. Russell. The following 



NO. 2050, \OI.. 7g] 



simple formula for the effective resistance R, per centi- 

 metre length, of the inner conductor of a concentric main 

 for high-frequency currents is obtained : — 



R = (ptnJ2Tra) (0-7071 + i(2ma + o-26s/ni-a= — 0-35/ in'a'), 



where p is the volume resistivity of the conductor, a its 

 r.'idius, ;i!" = S?r"/i//p, /a the permeability of the conductor, 

 and / the frequency of the alternating current. This 

 formula may be used in wireless telegraphy for calculating 

 the resistance of a conductor when other conductors carry- 

 i[ig high-frequency currents are not too close. For values 

 of ma greater than b the maximum inaccuracy of the 

 formula is less than i in 10,000. In obtaining the solu- 

 tion, exact formulje are obtained for the density of the 

 current at all points on the inner and outer conductors. — 

 Note on the luminous efficiency of a black body : Dr. 

 C. V. Drysdale. The importance of efficient methods of 

 light production renders it of interest to ascertain the 

 possibilities of a black body as a light radiator at various 

 temperatures, and the author has attempted to obtain these 

 from the radiation formula of Wien. The energy radiated 

 between any two wave-lengths is written down, and the 

 total radiation calculated. This, in conjunction with Kurl- 

 baum's determination of the radiation constant, and 

 Lummer and Pringsheim's results, gives rise to the 

 formulae given in the paper. .A table and curves calcu- 

 lated from these formulae have been worked out by Mr. 

 A. F. Burgess, and show the relation of the total and 

 luminous radiation and luminous efficiency for various 

 temperatures. The comparison of the luminous energy so 

 calculated with the intensity of light radiation found by 

 Prof. F^ry leads to a mechanical equivalent of light of 

 about 0-075 watt per candle, which is a fairly probable 

 figure. The results show the enormous extent to which 

 the luminous efficiency is dependent upon the temperature, 

 and how extremely low it is at ordinary temperatures. At 

 1500° C. the efficiency is only of the order of i per cent, 

 or less, while at 2000° C. it is about 3 per cent. The 

 highest efficiency is obtained at a temperature of about 

 6500° C, and is then only between 40 per cent, and 50 per 

 cent. This strongly points to the necessity for working 

 in the direction of selective radiation or luminescence. — 

 The use of the potentiometer on alternate current circuits : 

 Dr. C. V. Drysdale. The great difficulty in alternate 

 current measurement lies in the shortness of the range of 

 the instruments available, and there is therefore a great 

 need for some instrument which, like the direct potentio- 

 meter, should be capable of measuring P.Ds. and currents 

 of any range with accuracy. By interposing an ammeter 

 on the dynamometer principle in the main circuit of a 

 potentiometer and deriving the current from the secondary 

 of a phase-shifting transformer, it is possible to check the 

 instrument with direct current against the standard cell in 

 the ordinary way, and then to reproduce the same current 

 in the poteiitiometer circuit and to bring it into coincidence 

 of phase with the P.D. to be measured. Experiments have 

 been made with this device by Mr. A. C. Jolley and the 

 author, first as to the accuracy of current measurement 

 using an ordinary low-resistance standard, and have been 

 found to give very good agreement with a Kelvin balance. 

 Other tests have been made to obtain the vector difference 

 of potential across a resistance coil and a choking coil 

 connected in series, and the triangle of voltages so formed 

 was found to, be very nearly closed. The tests so far made 

 seem to indicate that an alternate current P.D. of o-i volt 

 ran be measured to an accuracy of 0-2 per cent, or closer. 

 The author has also designed a universal potentiometer on 

 this principle which serves both for direct- and alternate- 

 current measurements, and for testing P.D., current, phase, 

 power, inductance, capacity, &c. 



Royal Anthropological Institute, January 26. — Annual 

 general meeting. — Prof. W. Ridgeway, president, in the 

 chair. — Anniversary address, the relation of anthropology 

 to classical studies ; Prof. Ridg-eway. The results that 

 had followed from the use of the anthropological method in 

 the study of the classics were pointed out. Subjects which 

 had long been obscure or had given rise to wild specula- 

 tions, in the light of anthropology took upon themselves 

 a clear meaning. For example, .Aristotle's account of the 

 origins of Greek society, an account which had for long 



