October 14, 1909] 



NA TURK 



471 



read a paper on the secondary rays excited in different 

 metals by a rays. He finds that the secondary rays 

 emitted by a selected metal when bombarded by the 

 a particles from polonium deposited on copper are pro- 

 portional to the a radiation, but that different metals are 

 not equally active, the secondary radiation varying from 

 (12 for platinum to 47 for aluminium. S radiation excited 

 by polonium appears to be independent of the metal which 

 carries the polonium, and is probably produced by and 

 accompanies the a particle in the course of its expulsion 

 from the polonium atom. Prof. McLennan continued with 

 a paper by Mr. V. E. Pound, on some phenomena 

 associated with the radiations from polonium. By 

 measuring the electrical charge acquired by an insulated 

 metal plate B placed close to and facing an insulated 

 copper plate .\ bearing a deposit of polonium, it was made 

 clear with the aid of moderate electric and magnetic 

 fields that there are present (i) a rays emitted by the 

 plate A ; (2) an easily absorbed secondary negative radia- 

 tion emitted by B ; and C3) an easily absorbed 5 radiation 

 emitted by \. An additional negative stream seemed to 

 arise from the polonium in stronger fields ; from its 

 behaviour it is considered to consist of streams of rest- 

 atoms from the active product RaG or polonium. Dr. O. 

 Reichenheim followed with an important paper, ordered 

 to be printed in cxtenso, on anode rays and their spectra. 

 He explained that the conditions for the production of 

 anode rays, or striction-anode rays, are : — (i) the presence 

 of positive ions, produced by heated salts of the alkalis 

 or alkaline earths serving as anode; (2) a high fall of 

 potential at the anode, which is produced by the presence 

 of halogen vapours in the tube, and is the origin of the 

 high velocity acquired by the ions, so that they appear as 

 rays in the tube. A new kind of positive rays passes 

 through a perforated anode under a high gradient of poten- 

 tial. These are called Aj rays, because they arc analogous 

 to the K, rays or retrograde rays which leave the kathode. 

 The spectra of anode rays are very simple, often simpler 

 than the arc or spark spectra. The rays show the Doppler 

 effect ; in the case of the earth-alkaline rays shifted lines 

 only were found, without any line in the unshifted position. 

 This seems to arise from the fact that we have here to 

 deal with moving particles which emit other lines than 

 the surrounding luminescent gas. A paper by Dr. H. L. 

 p.ronson and Mr. A. N. Shaw, on Clark and Weston 

 standard cells, was taken as read owing to lack of time. 

 It dealt with the accuracy and reproducibility of these 

 cells. The mean of five set up in the National Physical 

 Laboratory differs from the mean of the cells set up in 

 Montreal by 5 microvolts. The maximum deviation of 

 their own cells from their mean was only 31 microvolts. 

 The ingredient of main importance is the mercurous 

 sulphate. The ratio of their Weston cells to their Clark 

 cells is 0-716953 as against the value 0716958 determined 

 by Wolff and Waters. Prof. Rutherford concluded with a 

 paper on the action of a rays upon glass, in w'hich he 

 detailed results analogous to the naturally occurring action 

 due to specks of beryl in rock which had been micro- 

 scopically detected by Prof. Joly. 



In the department of cosmical physics, which met 

 simultaneously, Dr. L. A. Bauer gave a risumi of some 

 of the chief results of interest obtained in the magnetic 

 work of the past ten years carried out under his direction 

 by the U.S. Coast and Geodetic Survey and the Carnegie 

 Institute of Washington. 



From the detailed magnetic survey of the United States 

 he found that it would not be possible to represent the 

 observed quantities satisfactorily by a general series of 

 spherical harmonics without using a prohibitive number of 

 terms. He found, moreover, by calculating the line 

 integral of the magnetic force around closed circuits, one 

 of which enclosed the whole of the United States, that a 

 part of the magnetic force, 1/300 to 1/500, must be due 

 to non-potential systems, e.^^. vertical electric currents. 

 Further calculations to test the existence of such currents 

 are being made with the data obtained by the Carnegie 

 Institute in the Pacific, 1905-S, and with the recent 

 resumption of the ocean magnetic w-ork by the Carnegie 

 it will soon be possible to make some circuits completely 

 round the earth. 



Various types of magnetic disturbances recorded at the 



NO. 2085, VOL. 81] 



live coast and geodetic survey observatories were briefly 

 discussed. An investigation of the relation between solar 

 activity and terrestrial magnetism, carried on in coopera 

 tion with Prof. G. E. Hale, showed that the absolute- 

 magnetic effect, connected apparently with an increase in 

 solar activity, is equivalent in general to a diminution in 

 the earth's mean intensity of magnetisation. Between 

 February i, 1907, and February i, igoS, this amounted 

 to about i/ioooth part. 



The author emphasised the need in such researches of 

 including all the magnetic elements and of differentiating 

 between effects resulting from internal and external 

 magnetic systems. 



Mr. R. F. Stupart read a paper on the distribution of 

 pressure over Canada. He pointed out that the world 

 charts of pressure distribution give an inadequate and 

 even inaccurate representation of the pressure conditions in 

 the dominion. He found that relatively high pressure in 

 the north-west at Dawson City is accompanied by re- 

 latively mild winters, and low pressure by severe winters, 

 a fact which is directly contrary to the prevailing idea that 

 in winter the higher the pressure the lower the tempera- 

 ture over continental areas. Dr. Shaw read a paper, by 

 Mr. J. I. Craig, on the surface motion of air in certain 

 circular storms. The paths of the air in travelling storms 

 were obtained from theoretical considerations, and com- 

 pared with the paths found by actual observation. 



Mr. J. W. Shipley showed photographs of large hail- 

 stones observed in western Canada shortly before the 

 meeting. In the centre of one of the stones he discovered' 

 a small fly which had apparently been carried upwards 

 and had formed a nucleus of condensation. 



Dr. A. A. Rambaut detailed some of the results of 

 stellar paralla.x observations carried out at the Radcliffe 

 Observatory, Oxford, with the equatorial instrument 

 acquired about six years ago employing Kapteyn's photo- 

 graphic method. The immediate object of the research 

 was to demonstrate the feasibility of a photographic 

 " Durchmusterung " for parallax extending to stars of the 

 thirteenth and fourteenth magnitude. A paper by Messrs. 

 Plaskett and Harper on two curiously similar spectroscopic 

 binaries concluded the sitting. 



On Monday, August 30, the section met in undivided' 

 sessions, which began with a discussion on positive elec- 

 tricity, opened by the president of the association. Sir 

 J. J. Thomson. The questions he asked were : — (i) Is 

 there a definite unit of positive electricity? (2) What is 

 its size? The same negative units are obtainable from 

 both oxygen and hydrogen ; is the same true for positive 

 electricity? .Attention is concentrated on kanalstrahlen and' 

 on the motion of positive ions through mixed gases. Sir 

 Joseph Thomson outlined the evidence afforded by the 

 magnetic and electric behaviour of the kanalstrahlen. He- 

 concludes that the ratio ejm is the same for the positive 

 rays of all gases and vapours (including uranium chloride)' 

 at very low" pressures, although at high pressures it does 

 depend upon the nature of the gas, and that therefore 

 there is a positive unit of electricity. This is confirmed 

 bv Wellisch's experiments on the velocity of the positive 

 ions through mixed gases ; their velocity is the same whether 

 they arise from hydrogen or from methyl-iodide. The value 

 of ejm is of the order of lo'' ; no evidence of smaller particles 

 has been obtained. Some observers, on the other hand, 

 find easily deflected positive rays. It must be remembered' 

 that the magnetic field mav alter the conditions of the 

 starting of rays, and, secondly, that deflection depends, not 

 onlv upon ejm, but also upon the velocity ; the easily 

 deflected rays are probably secondary rays. In the dis- 

 cussion which followed many points were raised dealing with 

 side-issues, but the main question did not receive much 

 fresh elucidation, and in the end the predominant feeling 

 was probablv that we are still a long way from obtainini^ 

 as definite experimental knowledge of positive electricity 

 as we at present possess of negative. 



Mr. A. S. Eddington next read a paper on the law 

 of distribution of stellar motions, in which he obtains the 

 constants of Schwarzschild's velocitv ellipsoid by making 

 use of the mean proper 'motions of stars instead of the 

 numbers of stars moving in the various directions as the 

 observed data. The following sufficiently exact result is 

 stated. The radius of the velocity ellipse in the direction 



