62 2 



NA TURE 



[October 29, 1903 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he undertake 

 to return, or to correspond with the writers of, rejected 

 manuscripts intended for this or any other part of Nature. 

 No notice is taken of anonymous communications.} 



Heating Effect of the Radium Emanation. 



In connection with the discovery of P.' Curie and Laborde 

 that radium continuously emits heat at a rapid rate, an 

 interesting question arises as to whether the heat emission 

 is directly connected with the radio-activity of that element 

 or is independent of it. 



To settle this point we have performed the following 

 experiments. The heating effect of 30 milligrammes of pure 

 radium bromide was first measured in a differential air 

 calorimeter. The radium bromide was then heated to a 

 sufficient temperature to drive off the emanation, and the 

 latter was condensed by passing through a short glass tube 

 immersed in liquid air, and then the tubes were sealed off. 

 On testing the de-emanated radium, the heating effect 

 diminished rapidly during the first few hours, and fell to a 

 minimum corresponding to about 30 per cent, of the original 

 value and then slowly increased again. On substituting 

 the emanation tube in the calorimeter, the heating effect at 

 first increased for a few hours to a maximum corresponding 

 to about 70 per cent, of the original heat emission of the 

 radium and then slowly decayed with the time. 



At any time after removal of the emanation, the sum of 

 the heating effect of the de-emanated radium anJ of the 

 emanation was found to be the same as that of the Original 

 radium. Experiments are still in progress to determine the 

 rate of recovery and loss of heating power of the de- 

 emanated radium and the separated emanation respectively, 

 but so far as the observations have gone, the curves of 

 decay and recovery are the same as those for the corre- 

 sponding o radiation. 



It has been shown (Rutherford and Soddy, Phil. Mag., 

 May) that, if the emanation is removed from radium, the 

 activity of the radium decays in the course of a few hours 

 to about 25 per cent, of its original value. This residual 

 activity consists entirely of a rays. The solid radium com- 

 pound regains its original activity after the lapse of about 

 one month. Immediately after the separation of the eman- 

 ation the activity (tested in a sealed vessel) rises to about 

 twice its original value, due to the production of excited 

 activity on the walls of the vessel, and then slowly decays 

 with the time, falling to half value in about four days. 

 At any time after removal of the emanation the sum total 

 of the activity of the radium and the emanation has a value 

 equal to that of the original radium. 



There is thus an exact parallel between the variation in 

 radiating power (measured by the o rays) and the heating 

 effect. In order to be sure how much of the emanation was 

 removed by heating, control experiments were made on the 

 y rays from the radium and the separated emanation. This 

 was tested by observing the rate of discharge of an electro- 

 scope after the rays had passed through 5 cm. of lead. In 

 some preliminary experiments by one of us last year it was 

 found that the y rays from radium appeared at the same 

 time as j8 rays, and were always proportional to them. 

 From these results it was deduced that all but 6 per cent, 

 of the emanation was removed by the heating. 



It is thus seen that the heating effect of radium directly 

 accompanies the o radiation from it, and is always pro- 

 portional to it, and that more than two-thirds of the heat- 

 ing effect is not due to the radium at all, but to the radio- 

 active emanation which it produces from itself. This 

 result accounts for the variation of heat emission with age 

 observed by the Curies, an account of which was given by 

 Prof. Dewar at the British Association. 



The amount of emanation from 30 milligrammes of 

 radium bromide, when collected in the tube, was sufficient 

 to cause a bright phosphorescence in the tube, but it was 

 too small either to measure or weigh. The amount of heat 

 emitted from the radium emanation is thus enormous com- 

 pared with the amount of matter involved. It seems prob- 

 able that the greater part of the heating effect of radium 

 13 a direct consequence of the expulsion of o rays. It still 



NO. 1774, VOL. 68] 



remains to be shown in what proportion the radiated energy 

 is distributed between the projected o particles and the 

 systems from which they are expelled. 



The results given here are at once explained on the dis- 

 integration hypothesis (Rutherford and Soddy, Phil. Mag., 

 May), in which the heat is considered to be derived from 

 the internal energy of the atom. On the view held by some 

 that radium gains its heat from an external source, it would 

 be necessary to suppose that less than a third of the heat 

 is due to the radium itself, and that the other two-thirds 

 are due to the radium emanation which is being con- 

 tinuously produced, and the power of which of absorbing 

 energy from an external source decays with the time. 



E. Rutherford. 

 H. T. Barnes. 



McGill University, Montreal, October 16. 



Papers and Procedure at the British Association. 



At the recent meeting of the British Association at South- 

 port I heard numerous complaints (repetitions of those I 

 have heard at not a few previous meetings) by the general 

 public, members of the Association, on the too technical 

 character of the papers read before it. These complaints 

 referred to all the sections except, perhaps, those of anthro- 

 pology, geography, and educational science. One over- 

 heard too often to be pleasant such remarks as " I am 

 interested in zoology, but what is the good of coming to 

 listen to such a paper as this? I have no idea what the 

 speaker is talking about " — the paper, in one specific in- 

 stance, was cytological, and of great value undoubtedly ; 

 and, " I have not gained much by becoming a member of 

 the Association; the papers are all over my head." These 

 complaints are being made by well educated men and women 

 interested in science, but not versed in its technicalities. 



Believing that this feeling in reference to the subjects 

 brought before the various sections is growing, and is, 

 moreover, not ill-founded, I venture, as a member of twenty 

 years' standing, to direct serious attention through your 

 columns to its existence, and to advocate some change in 

 the character of the papers accepted for reading before the 

 Association, so that the objects for which this great society 

 was founded may be more fully attained as regards the 

 general public of the town visited, on the support of which 

 the Association is so largely dependent. 



Purely technical papers which appeal only to the specialist 

 in chemistry, biology, engineering, or physics, are out of 

 place before an audience the majority of whom are not 

 specialists, but who have become members for the occasion 

 in the hope of listening to an understandable exposition of 

 the subject by the men who have contributed to making 

 that section of science. Such purely technical papers should 

 be reserved for the societies which exist for the cultivation 

 of that particular subject. The British Association should 

 either become a purely scientific society or become more 

 what it was established for, an association for the advance- 

 ment of science among the people, at which the results of 

 the investigations of the year are, as it were, summed up 

 and presented to the members, both specialists and those of 

 the general public interested in science, in language which 

 the whole audience can understand. An author, instead of 

 going into the details of the various intricate investigations 

 and experiments he has made — which can often enough be 

 followed fully only by his fellow-workers in that particular 

 section of his subject — should far more than heretofore deal 

 broadly with the results obtained, indicating their value to 

 the particular subject, and their bearing on his own or other 

 departments of knowledge. The general public have really 

 some cause for complaint that their subscription has been 

 obtained from them on a misunderstanding. If the Associ- 

 ation is to become more and more a purely scientific society, 

 then the fact should be made more widely known, so that 

 disappointment may not be needlessly caused to those who 

 join it. In that case, moreover, there would be no need 

 of the publicity with which the Association meets at the 

 various towns it visits. It might quietly assemble at the 

 chosen town in rooms hired or lent for the purpose, and 

 associate itself only with the specialists of the place. 



Liverpool, October 20. Henry O. Forbes. 



