324 



NA TURE 



[August 2, 1906 



duces a destruction of the skin and flesh over a small 

 area — in fact, a sore place. (2) The smallest trace of 

 radium brought into a room where a charged electroscope 

 is present, causes the discharge of the electroscope. .So 

 powerful is this electrical .nction of radium that a very 

 sensitive electrometer can detect the presence of a quantity 

 of radium five hundred thousand times more minute than 

 that which can be detected by the spectroscope (that is 10 

 say, by the spectroscopic e.xamination of a flame in which 

 minute traces of radium are present). (3) Radium actually 

 realises one of the properties of the hypothetical stone to 

 which I compared it, giving out light and heat. For it 

 does give out heat which it makes itself incessantly and 

 without appreciable loss of substance or energy (" appreci- 

 able " is here an important qualifying term). It is also 

 faintly self-luminous. Faii'ly sensitive thermometers show 

 that a few granules of radium salt have always a higher 

 temperature than that of surrounding bodies. Radium has 

 been proved to give out enough heat to melt rather more 

 than its own weight of ice every hour ; enough heat in one 

 hour to raise its own weight of water from the freezing- 

 point to the boiling-point. After a year and six weeks a 

 gram of radium has emitted enough heat to raise the 

 temperature of a thousand kilograms of water one degree. 

 And this is always going on. Even a small quantity of 

 radium diffused through the earth will suffice to keep up 

 its temperature against all loss by radiation ! If the sun 

 consists of a fraction of one per cent, of radium, this will 

 account for and make good the heat that is annually lost 

 by it. 



This is a tremendous fact, upsetting all the calculations 

 of physicists as to the duration in past and future of the 

 sun's heat and the temperature of the earth's surface. 

 The geologists and the biologists have long contended that 

 some thousand million years must have passed during 

 which the earth's surface has presented approximately the 

 same conditions of temperature as at present, in order to 

 allow time for the evolution of living things and the form- 

 ation of the aqueous deposits of the earth's crust. The 

 physicists, notably Prof. Tait and Lord Kelvin, refused to 

 allow more than ten million years (which they subsequently 

 increased to a hundred million) — basing this estimate on 

 the rate of cooling of a sphere of the size and composition 

 of the earth. They have assumed that its material is self- 

 cooling. But, as Huxley pointed out, mathematics will 

 not give a true result when applied to erroneous data. It 

 has now, within these last five years, become evident that 

 the earth's material is not self-cooling, but on the contrary 

 self-heating. And away go the restrictions imposed by 

 physicists on geological time. They now are willing to give 

 us not merely a thousand million years, but as many more 

 as we want. 



And now I have to mention the strangest of all the 

 proceedings of radium — a proceeding in which the other 

 radio-active bodies, actinium and thorium, resemble it. 

 This proceeding has been entirely Rutherford's discovery 

 in Canada, and his name must be always associated with 

 it. Radium (he discovered) is continually giving off, apart 

 from and in addition to the rectilinear darting rays of 

 Becquerel — an " emanation " — a gaseous " emanation." 

 This " emanation " is radio-active — that is, gives off 

 Becquerel rays — and deposits " something " upon bodies 

 brought near the radium, so that they become radio-active, 

 and remain so for a time after the radium is itself removed. 

 This emanation is always being formed by a radium salt, 

 and may be most easily collected by dissolving the salt in 

 water, when it comes away with a rush, as a gas. Sixty 

 milligrams of bromide of radium yielded to Ramsay and 

 Soddy 0-124 (or about one-eighth) of a cubic millimetre of 

 this gaseous emanation. What is it? It cannot be de- 

 stroyed or altered by heat or by chemical agents ; it is a 

 heavy gas, having a molecular density of 100, and it can 

 be condensed to a liquid by exposing it to the great cold 

 of liquid air. It gives a peculiar spectrum of its own, and 

 is probably a hitherto unknown inert gas — a new element 

 similar to argon. But this by no means completes its 

 history, even so far as experiments have as yet gone. The 

 radium emanation decays, changes its character altogether, 

 and loses half its radio-activity every four days. Precisely 

 at the same rate as it decays the specimen of radium salt 



NO. 1918, VOL. 74] 



from which it was removed forms a new quantity of 

 emanation, having just the amount of radio-activity which 

 has been lost by the old emanation. All is not known 

 about the decay of the emanation, but one thing is abso- 

 lutely certain, having first been discovered by Ramsay and 

 Soddy and subsequently confirmed by independent experi- 

 ment by Madame Curie. It is this : After being kept three 

 or four days the emanation becomes, in part at least, con- 

 verted into helium — the light gas (second only in the list 

 of elements to hydrogen), the gas found twenty-five years 

 ago by Lockyer in the sun, and since obtained in some 

 quantities from rare radio-active minerals by Ramsay ! 

 The proof of the formation of helium from the radium 

 emanation is, of course, obtained by the spectroscope, and 

 its evidence is beyond assail. Here, then, is the partial 

 conversion or decay of one element, radium, through an 

 intermediate stage into another. And not only that, but 

 if, as seems probable, the presence of helium indicates the 

 previous presence of radium, we have the evidence of 

 enormous quantities of radium in the sun, for we know 

 helium is there in vast quantity. Not only that, but inas- 

 much as helium has been discovered in most hot springs 

 and in various radio-active minerals in the earth, it may 

 be legitimately argued that no inconsiderable quantity of 

 radium is present in the earth. Indeed, it now seems 

 probable that there is enough radium in the sun to keep 

 up its continual output of heat, and enough in the earth 

 to make good its loss of heat by radiation into space, for 

 an almost indefinite period. Other experiments of a similar 

 kind have rendered it practically certain that radium itself 

 is formed by a somewhat similar transformation of uranium, 

 so that our ideas as to the permanence and immutability 

 on this globe of the chemical elements are destroyed, and 

 must give place to new conceptions. It seems not improb- 

 able that the final product of the radium emanation after 

 the helium is removed is or becomes the metal lead ! 



It must be obvious from all the foregoing that radium 

 is very slowly, but none the less surely, destroying itself. 

 There is a definite loss of particles which, in the course of 

 time, must lead to the destruction of the radium, and it 

 would seem that the large new credit on the bank of time 

 given to biologists in consequence of its discovery has a 

 definite, if remote, limit. With the quantities of radium 

 at present available for experiment, the amount of loss of 

 particles is so small, and the rate so slow, that it cannot 

 be weighed by the most delicate balance. Nevertheless it 

 has been calculated that radium will transform half of 

 itself in about fifteen hundred ye.-^rs, and unless it were 

 being produced in some way all the radium now in 

 existence would disappear much too soon to make it an 

 important geological factor in the maintenance of the 

 earth's temperature. As a reply to this depreciatory state- 

 ment we have the discovery by Rutherford and others that 

 radium is continually being formed afresh, and from that 

 particular element in connection with which it was dis- 

 covered — namely, uranium. Hypotheses and experiments 

 as to the details of this process are at this moment in full 

 swing, and results of a momentous kind, involving the 

 building-up of an element with high atomic weight by the 

 interaction of elements with a lower atomic weight, are 

 thought by some physicists to be not improbable in the 

 immediate future. 



The delicate electric test for radio-activity has been 

 largely applied in the last few years to all sorts and con- 

 ditions of matter. As a result it appears that the radium 

 emanation is always present in our atmosphere ; that the 

 air in caves is especially rich in it, as are underground 

 waters. Tin-foil, glass, silver, zinc, lead, copper, platinum 

 and aluminium are, all of them, slightly radio-active. The 

 question has been raised whether this widespread radio- 

 activity is due to the wide dissemination of infinitesimal 

 quantities of strong radio-active elements, or whether it is 

 the natural intrinsic property of all matter to emit Becquerel 

 rays. This is the immediate subject of research. 



Over and above the more simply appreciable facts which 

 I have thus narrated, there comes the necessary and diffi- 

 cult inquiry. What does it all mean? What are the 

 Becquerel rays of radio-activity? What must we conceive 

 to be the structure and mechanism of the atoms of radium 

 and allied elements, which can not only pour forth ceaseless 



