-'58 



NATURE 



[May 24, 19 1 7 



been prematurely eclipsed." This generous esti- 

 mate of the part men of science have taken in 

 the war is noteworthy. "It has been a war of 

 chemists, of engineers, of physicists, of doctors. The 

 professor and lecturer, the research assistant, and the 

 research student have suddenly become powerful assets 

 to the nation. Whatever university you may choose 

 to visit, you will find it to be the ^cene of delicate and 

 recondite investigations, resulting here in a more 

 deadly explosive, there in a stronger Arjiiy boot, or 

 again in some improvement to the fast-advancing 

 technique of aerial navigation." The brochure de- 

 serves to be widely read. Its price is \s. net. 



SOCIETIES AND ACADEMIES. 

 London. 

 Royal Society, May 10. — S'r J. J. Thomson, presi- 

 dent, in the chair. — Sir Joseph Larmor and N. 

 Yamaga : Permanent periodicity in sun-spots. A dis- 

 cussion of the more sharply marked phases of the 

 curve of frequency of sun-spots, since 1750, led New- 

 comb, in 190 1, to strong confirmation of the prevalent 

 view, previously verified by Wolf and by Wolfer, that 

 sun-spots are governed by some permanent periodic 

 agency of period determined very closely by him as 

 11-13 ±o-02 years, and more recent independent dis- 

 cussions, by Wolfer in 1902 and by Schuster in 1906, 

 have led them to conclusions nearly identical. The^ 

 form of this periodic component is here extracted by' 

 semi-graphical methods, such as are appropriate to a 

 permanent unbroken period, and also provide a 

 further ch^k on the degree of validity of the result. 

 The periodic feature is found to be strongly and 

 definitely present, provided the records for the two 

 sun-spot cycles from about 1776 to 1798, which would 

 largely vitiate it, are rejected as untrustworthy, or 

 else are almost wholly assigned to some strong but 

 transient anomaly. The residue of the sun-spot curve, 

 when this periodic part is removed, seems to be acci- 

 dental and sporadic, showing no other permanent 

 periodicity of comparable period. The periodogram 

 analysis of .Schuster had, in fact, already led him to 

 the result that the record is not homogeneously con- 

 stituted even in the wider sense appropriate to natural 

 radiation. The Fourier series here determined for 

 the i>eriodic part is fcRmd to be composed of sines 

 only within the limits of attainable accuracy ; thus 

 the graph of that part is made up of anti-symmetrical 

 undulations, a feature which mav form a clue to its 

 physical <?rigin In the sun.— Prof. G. W. O. Howe ; 

 The high-frequencv resistance of multiple-stranded 

 insulated wire. The conductors employed In radio- 

 telegraphy are frequently made up of a large number 

 of fine wires separately insulated and stranded or 

 plaited together in such a way that every wire occupies 

 in turn the same relative position In the multiple con- 

 ductor. In this wav the total current Is forced to 

 distribute Itself equally between all the wires, even at 

 high frequencies. The object of this is twofold, viz. 

 to make the Inductance Independent of frequency and 

 to reduce the resistance at high frequencies. It is 

 shown In this paper that the second object is rarely 

 achieved because of the eddy currents Induced in the 

 wires by the maenetic flux within the conductor. It 

 Is shown also that the loss due to this cause is so great 

 that the effective resistance of the stranded conductor 

 is In manv cases, greater than that of the solid wire 

 which could be put In Its place. In the first part of 

 the paper formulae are deduced on the assumption that 

 the eddv currents in the fine wires do not apnrec'nbK- 

 affect the distribution of magnetic flux within them. 

 Tn the second part this assumption Is not made and 

 formulae are, deduced vhlch take into account the 



NO. 2482, VOL. 99] 



screening effect of the eddy currents. It is proved, 

 however, that the assumption is permissible in nearly 

 all the cases considered. A number of tables are 

 given showing the ratio of the high frequency to the 

 continuous current resistances of straight aind coiled 

 conductors of different sii'es made up of fine wires of 

 three alternative diameters. These formulae and 

 tables enable one to see at once if any advantage Is 

 to be gained by using such a stranded conductor In 

 any given case, and, if so, the best number of wires 

 and space-factor to employ. The paper shows con- 

 clusively, however, that the extended use of such con- 

 ductors in radio-telegraphy for the purpose of reduc- 

 ing the resistance has no scientific justification. 



Physical Society, April 27. — Prof. C. V. Boys, presi- 

 dent, In the chair.— Prof. J. A. Fleming : A note on the 

 derivation of the general equation for wave motion in 

 an elastic medium. The paper explains a simple 

 method of arriving at the general differential equation 

 for wave motion, viz. 

 ^0 



df' \ dx' dy^ dz' f 



where c is the velocity of propagation of the wave. 

 The method described may be epitomised by say- 

 ing that the differential equation is obtained by equat- 

 ing the product of strain-acceleration d^<p/dt'^ and 

 density to the static measure of the stress expressed 

 as the space variation of the product of the elasticity 



and the strain slope (^^), which is the proper 



measure of the stress at the point considered. — A. 

 Johnstone : The effect of stretching on the thermal con. 

 ductivity of wires. For all the wires used (copper, 

 steel, nickel, aluminium, brass, zinc), stretching pro- 

 duced a slight increase in thermal conductivity. The 

 most satisfactory experiments showed an increase of 

 about 05 per cent for a tension of about 07 of the 

 elastic limit. After the tension was withdrawn the 

 conductivity retur.ied approximately to Its original 

 value. — Prof. H. Chatley : Cohesion (third paper), 'the 

 objects of the paper are: — (a) To re-state and add 

 further evidence In favour of an electrical theory of 

 cohesion, (b) To provide tentative empirical formulae 

 for the expression of intermolecular forces. The 

 author defines cohesion as the net attraction {i.e. 

 balance of attraction over repulsion) between molecules 

 which are relatively chemically saturated, at distances 

 not greatlv exceeding the molecular diameters, snd the 

 following formula Is proposed for this attraction : — 

 ;^o = G//i'id^^'^^'^'>^^, "^'iriere G Is the Newtonian constant 

 of gravitation, ni the molecular mass, d the molecular 

 interval (centre to centre), and d^ is the molecular 

 diameter. 



Royal Astronomical Society, Mav 11. — Major P. A. 

 MacMahon, president, in the chair. — Dr. J. L. E. 

 Dreyer : The origin of Ptolemy's Catalogue of Stars. 

 For more than a century It had been the prevailing 

 opinion that Ptolemy had borrowed all his star places 

 from the catalogue of Hipparchus, merely -adding a 

 constant quantity to the longitudes to bring them up 

 to his own epoch. It was contended that this opinion 

 was Ill-founded; that the catalogue of Hipparchus 

 could not have contained more than 850 stars, so that 

 Ptolemy could not have borrowed from Hipparchus the 

 whole of his catalogue of 1025 stars. There appeared 

 no reason for disbelieving Ptolemy's statement that 

 he had himself made extensive observations of the 

 fixed stars.^Dr. S. Chapman : (i) Convection and diffu. 

 slon within giant stars. Prof. Eddington had shown 

 that In a giant star of low density the temperature 

 and pressure gradients towards the centre must be 

 much less than formerly supposed, the Influence of 

 gravitv being largely counteracted by radiation pres- 



