October 27, 1904] 



NA TURE 



639 



Dr. Glazebrook, and Prof. Perry as delegates, also con- 

 sidered the questions of units and standards, and at the 

 concluding meeting of the congress the announcement was 

 made that the chamber of Government delegates had decided 

 to advise their respective Governments to appoint a 

 j)ermanent International commission, consisting of two 

 members from each Government, to secure uniformity in 

 units and nomenclature, and a second committee to deal 

 with the international standardisation of machines, this 

 latter to act by correspondence. 



The most interesting paper on radio-activity was that 

 of Prof. Rutherford, who traced one step further his re- 

 mari<able disintegration theory of radio-activity. Starting 

 with the radium emanation, he traced its disintegration 

 through three stages, which he called radium A, B, and C, 

 ihe latter producing by its disintegration o, ;3, and 7 rays. 

 These changes take place fairly rapidly, and the activity 

 dies away approximately following a logarithmic law. 

 There remains behind, however, in the tube which contained 

 the emanation a deposit the activity of which dies away 

 very much more slowly. By dissolving this deposit in 

 sulphuric acid, it can be separated into two pans, the one 

 of which will deposit on a bismuth disc immersed in the 

 liquid, and the second part will remain behind. That 

 which remains behind is found to give out /3 rays only, and 

 is called by Rutherford radium D, while that which is 

 deposited on the bismuth disc gives a rays only, and he 

 calls it radium E. He also finds that there is another way 

 of separating these two substances, namely, by heating the 

 deposit on platinum to 1000° C, at which temperature the 

 radium E is volatile and driven off. Regarding the rate of 

 decay of the activity of these two substances, Rutherford 

 estimates that the activity of radium D will fall to half value 

 in about forty years, while that of radium E will require only 

 about one year. By a comparison of the properties of radium 

 E with polonium, Rutherford deduced strong arguments in 

 favour of their identity, and he also considered that radio- 

 tellurium was the same. The product radium D is more 

 uncertain, though it may be radio-lead. If these results 

 are confirmed, and it is proved that polonium, radio- 

 tellurium, and radio-lead are all products of the disinte- 

 gration of the radium atom, a considerable simplification 

 will result, and a step forward in our knowledge of radio- 

 activity has been made. 



The papers by Elster and Geitel concerning natural radio- 

 activity of the atmosphere and the earth, and by Prof. 

 McLennan on the radio-activity of mineral oils and natural 

 gases, gave the results of large numbers of tests on the 

 radio-activity of various waters, oils, muds, &c., from 

 different parts of the earth's surface and from different 

 depths, and they go far to show the omnipresence of radio- 

 activity in the crust of the earth, though they are not yet 

 sulliciently advanced to settle the important question as to 

 whether there exists a large number of radio-active minerals 

 in the earth which have not yet been isolated. McLennan 

 deduces from the rate of decay of the emanation the con- 

 clusion that the active substances in natural gases, 

 petroleum, spring-water, and mercury are very probably 

 identical with the emanation from radium, and he also 

 mentions that there appears to be present in some samples 

 of crude petroleum an active substance more persistent than 

 the emanation from radium. Is this the radium D and E 

 of Rutherford? 



It was unfortunate that, whereas three important papers 

 on the arc were taken together in one section, the same 

 time was selected for Prof. Child to read his arc paper in a 

 different section, so that those interested in arc pKenomena 

 could not hear all the papers ; added to this, three out of the 

 four arc papers were not in print at the time of the 

 congress, and the acoustical properties of the rooms in which 

 the meetings were held were of the very worst, making It 

 almost impossible to hear the speakers. Prof. Child 

 attempted to explain the phenomena of the arc on a purely 

 ionic basis, which he summarised as follows : — " The 

 current is carried by ions. These ions are produced, first, 

 either within the kathode, because of its high temperature, 

 or at the boundary surface by the impact of the positive 

 ions I second, through the gas by the impact of the atoms 

 on the negative ions at high temperature ; and third, at the 

 boundary surface of the anode by the impact of the negative 

 ions." The theory is, however, not very satisfying, as it 



throws but little light on many important points, more 

 especially the actions going on at the surfaces of contact 

 of the vapour column and electrodes, as he admits. He 

 also does not attempt to explain the extraordinary effect of 

 slight traces of impurities, which is so marked in the casfe 

 of the carbon arc that the present writer is of the opinion 

 that with perfectly pure carbon electrodes the carbon arc, as 

 we know it, could not exist. 



One of the most interesting facts brought out in Prof. 

 Child's paper is the great importance of the temperature of 

 the kathode, and, as he says, " the essential condition 

 appears to be that the kathode shall be very hot." Prof. 

 .Stelnmetz entered very fully into the importance of the 

 kathode, and he described the stream of particles which he 

 considered as issuing from it. The existence of this stream, 

 and .Steinmetz's view that the re-lighting of the alternating 

 arc is a disruptive phenomenon, received striking confirm- 

 ation from Prof. Lombadi's stroboscopic photographs of 

 the arc. 



Prof. Stelnmetz deduced an equation for the relation 

 between the arc-length, P.D., and current from theoretical 

 reasoning, which took the form \' = a-i-b{l + c)! ,/ A, where 

 V is the P.O., A the current, and / the arc-length; he 

 applied this equation to the volt-ampere characteristics of 

 the magnetite arc, but the agreement between the observed 

 and calculated values seemed as if it would have been better 

 if Mrs. Ayrton's form of equation had been adopted. The 

 magnetite arc looks as if it has a large future before it, as 

 its efficiency is high and the rate of consumption of the 

 electrodes extremely slow. In this connection Prof. Steln- 

 metz said that he had obtained an efficiency of 0.15 watt 

 per mean spherical C.P. with a titanium arc, but that it 

 was not in a commercial form yet. Mr. Blondel, in his 

 paper on impregnated arc light carbons and lamps, gave 

 (if the figures were not misquoted in the reading) an equally 

 extraordinary result with his new lamp and carbons, namely, 

 a mean /lemi'spherical C.P. of 4800 for a 500 watt 9 ampere 

 lamp, as against 700 C.P. for an ordinary open arc taking 

 practically the same power. 



Dr. Flemipg and Dr. de Forest each contributed papers 

 on wireless telegraphy, and Dr. Guthe gave one on coherer 

 action ; there was also a highly mathematical paper on the 

 theory by Mr. Stone Stone. Dr. Fleming's paper gave a 

 good general rt'sitmd of the subject, but contained very little 

 new matter. The chief interest in de Forest's paper centred 

 in the experiments he describes to prove that the action of 

 his electrolytic receiver is due to polarisation, and not to a 

 heating of the electrolyte as alleged by Fessenden. The 

 electrolytic receiver consists essentially of a very small 

 electrode dipping into an electrolyte, the second electrode 

 being large and connected in series with a cell and tele- 

 phone. Normally, a very small current flows through the 

 receiver, which is greatly increased directly the oscillations 

 pass through it. Dr. de Forest maintains that this is 

 caused by the oscillations destroying the polarisation at the 

 small electrode, and one of the most conclusive statements 

 he makes in favour of this view is that the small electrode 

 must be made the anode, and that the receiver is practically 

 inoperative if it is connected to the negative of the 

 local battery. This would certainly not be the case if 

 the action depended on the heating of the electrolyte, 

 which should be independent of the direction of the local 

 battery. 



Dr. Guthe treated at length the theory of the action of 

 the coherer, especially from the electronic point of view. 

 The first step is assumed to be an electrostatic attraction 

 between the metallic particles. The electrons are carried 

 over from the negatively charged metal to the other side, 

 and we have a current carried entirely by the electrons. 

 .A.n increase in the electrical energy produces an increase 

 in the number of electrons, i.e. the current increases while 

 the difference of potential remains constant. This passage 

 of electricity is accompanied by a pressure at right angles 

 to the flow, which pushes aside the molecules of the dielectric 

 which may have been between the metallic particles, and 

 there remains what may be considered as a continuous 

 metallic conductor. Dr. Guthe further extends this theory 

 by considering the ionisation of the gas or dielectric 

 surrounding the metallic particles. Both Dr. Guthe's and 

 Dr. Fleming's papers contain numerous bibliographic refer- 



NO. 1826, VOL. 70] 



