May 2 1, 1908] 



NA TURE 



71 



February 20. — " Effects of Self-imluction in an^ Iron 

 Cylinder wh'rn traversed bv Alternating Currents." By 

 Trof. K. Wilson. Communicated by Sir William Preecc, 

 l-.R.S. 



Alternating currents up to about 2000 amperes at tre- 

 quencies varying from 1/45 to 1/360 were supplied to an 

 iron cylinder to inches in diameter, and the change of 

 magnetic induction at different depths was obtained from 

 readings taken with three dead-beat galvanometers con- 

 nected to coils threaded through holes in the cylinder. 

 The total current in the cylinder was observed on an 

 amperemeter in the circuit. The curves of E.M.F. in 

 the exploring coils were plotted, and by integration the 

 magnetic induction at different depths was obtained. The 

 results show that the effect due to internal self-induction, 

 commonly called "skin effect," is greater the greater the 

 average 'permeability, and it is shown how it depends 

 upon change of current and frequency. The phase dis- 

 placement of the E.M.F. curves reckoned from zerc) of 

 current diminishes with increase of current for a given 

 frequency, and increases with increase of frequency for a 

 given current. From the hysteresis loops of the material 

 the total currents interior to the respective radii were 

 found and plotted against radius as distribution curves, 

 from which the C-R loss was calculated. The hysteresis 

 watts were also found, and both compared with the watts 

 which would occur if the distribution under continuous 

 current were assumed to persist. For a given frequency, 

 the ratio of the C=R loss with alternating to those with 

 continuous currents is greater the higher the average 

 permeability. For a given current, the C-R loss increases 

 with frequency, and the hysteresis loss tends to increase 

 with frequency, but to diminish owing to increased skin 

 effect. The results hold for a cylinder of n times the 

 diameter if the current is varied as n, and the frequency 

 hnversely as vr. The paper contains tables of figures and 

 curves. 



" On the Refractive Indices of Gaseous Nitric Oxide, 

 Sulphur Dioxide, and Sulphur Trioxide." By C. 

 Cuthbertson and E. Parr Metcalfe. Communicated by 

 Prof. F. T. Trouton, F.R.S. 



The refractive index of nitric oxide, purified by fractiona- 

 tion at low temperatures, was found to be 1.0002939 for 

 sodium light. This is about i per cent, less than the value 

 found by Mascart. 



The index of sulphur dioxide was re-determined in view 

 of the discrepancies between the numbers published by 

 previous observers. The value now obtained, 1.0006609, 

 is in agreement with the results of Ketteler and G. W. 

 Walker, when these are corrected for the density of the 

 gas at o" C. and 760 mm. The index of sulphur trioxide 

 is, approximately, 1.000737. Both this and the index of 

 sulphur dioxide are considerably below the additive values. 



Faraday Society, April 28 — Prof A K. Huntington, vice- 

 president, in the chair. — The planimetric analysis of 

 alloys, and the structure of phosphor-copper : A. K. 

 Huntington and C. H. Deach. The conditions under 

 which it is possible to estimate the relative propor- 

 tions of the constituent metals in an alloy by means of 

 the planimetric measurement of the areas of the solid 

 phases exposed in a polished and etched micro-section 

 is discussed. Details of the method are given, and its 

 accuracy is shown by a series of measurements of analysed 

 alloys. The method has been most fully studied in the 

 case of phosphor-copper, of which a number of photo- 

 micrographs are shown. In the case of alloys containing 

 less than the eutectic proportion of phosphorus, however, 

 the area of copper crystals is found to be considerably 

 greater than that calculated from the composition deter- 

 mined by analysis. The origin of the discrepancies was 

 traced to the segregation of the eutectic, the copper 

 crystals which separate at first drawing to themselves a 

 portion of the copper of the surrounding eutectic. The 

 crystals are therefore surrounded by a belt of copper phos- 

 phide. By measuring the area of this belt, and thence 

 ■calculating the amount of segregated copper, a correction 

 may be applied to the area of the crystals, and a very 

 satisfactory agreement with the analytical results is thus 

 obtained. — The interaction of aluminium powder and 

 carbon : F. E. Weston and H. R. Ellis. Very little work 



has been done on the combination of aluminium and carbon 

 at temperatures lower than that of the electric furnace. 

 The authors now show that aluminium powder and carbon 

 can be made to react at temperatures much below that of 

 the electric furnace. Mixtures of aluminium powder and 

 carbon, wood charcoal, sugar carbon, and graphite have 

 been prepared, in which reaction takes place by starting 

 with a fuse of magnesium powder and barium peroxide, as 

 in Goldschmidt's reaction ; other mixtures have been made 

 which only react when heated at temperatures varying 

 from 400° C. to 1000° C. In all cases the products of 

 reaction were found to be aluminium carbide (9-12 per 

 cent, to 65-91 per cent.), aluminium nitride (3-67 per cent, 

 to 42-16 per cent.), alumina (11-07 per cent, to 55-4 per 

 cent.), aluminium, and carbon. The carbide produced is 

 most probably that described by Moissan as aluminium 

 carbide, C^.'M,, since the gas obtained on treating the pro- 

 duct of reaction with either water or hydrochloric acid was 

 found to consist of CH, and H, the latter coming fron\ 

 (1) the action of HCl in unaltered aluminium; (2) action 

 of NHj on aluminium, the NH,, being formed by the 

 action of water on aluminium nitride. 



Mathematical Society, Mav 14. — Prof. W. BurrsiHe, 

 [ir)-sid(-nt. In the chair. — The invariants of the general 

 linear homographic transformation in two variables : 

 Major P. .'\. MacMahon. — The order of the group of 

 isomorphisms of an Abejian group : H. Hilton. — The 

 calculation of the normal modes and frequencies of vibrating 

 s\'stems (preliminary note) : Prof. .V. E. H. Love. — .A 

 question In probability : Prof. J. E. .\. Stegg^all. 



P.4RIS. 



Academy of Sciences, May n. — M. H. Becquerd in the 



chair. — The president announced the death of M. Albert 

 de Lapparent. — .'\ planimeter permitting of the integra- 

 tion of the Abelian equation yy' = Ay- -f By -I- C : Col. 

 Jacob. This form of equation occurs in the study of 

 ballistics. — The application of the laws of similitude to 

 the propagation of detonations ; MM. Crussard and 

 Jouguet. — Wireless telegraphy with directed waves : MM. 

 Bellini and Tosi. The direction of the waves is obtained 

 by the use of aerial conductors formed of closed oscillating 

 circuits disposed in vertical planes without connection with 

 the earth. The transmitter was installed at Dieppe, and 

 two receiving posts were constructed, one at Havre and 

 the other at Harfleur. The signals could be transmitted 

 to either receiving station, and were received only 

 by the station to which they were directed. The 

 signals neither interfere with nor are interfered with by 

 other systems of wireless messages. — The range of the 

 a rays : William Duane. It has been shown by various 

 observers that tin- photographic, phosphorescent, and 

 ionising action of the a rays cease abruptly when the rays 

 have traversed a few centimetres in air, and in the present 

 paper experiments are described which were made with the 

 abject of deciding whether the other actions of these rays 

 cease at the same distance. From the form of the curves 

 obtained it is very difficult to decide the exact point at 

 which the range of the a rays ceases, but it was found 

 that the charge of the a particles and their ionisation 

 ceases at the same point. — The electric dispersion of water : 

 F. Beaulard. By extending the range of the method 

 previously described to other wave-lengths, there would 

 apnear. to be some anomalous electric dispersion for the 

 order of magnitude of the electric field studied. — The spec- 

 trum of iron observed in the flame of the ox>hydrogi>n 

 blow-pipe : G. A. Hemsalech and C. de Watteville. 

 Using the method previously described, the gases feeding 

 the flame were supplied with finely divided particles of the 

 metal torn from electrodes by the electric spark. A table 

 of the wave-lengths and intensities of the observed lines is 

 -given, and the results compared with the arc spectrum of 

 iron. — Contribution to the study of the photographic 

 grating: H. Calmels and L. P. Clerc. — Molecular agita- 

 tion and the Brownian movement : Jean i?errin. An 

 attempt to prove that molecular agitation is the cause of 

 the Brownian motion. It results from the proof given 

 that the number of molecules per gram of liquid is of the 

 order 6-7x10^^. — An electro-optic phenomenon in air con- 

 taining dust in suspension : Eugene Bloch. — The com- 

 mensurability of the atomic weights : M. Hinrichs. — 



N-'O. 20 1 2. VOL. 



78I 



