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SCIENCE 



[N. S. Vol. XXX. No. 765 



outside of the earth. This, as Rutherford 

 has pointed out, entirely vitiates the previ- 

 ous method of determining the age of the 

 earth. The fact is that the radium gives 

 out so much heat that we do not quite know 

 what to do with it, for if there was as much 

 radium throughout the interior of the earth 

 as there is in its crust, the temperature of 

 the earth would increase much more rap- 

 idly than it does as we descend below the 

 earth's surface. Professor Strutt has 

 shown that if radium behaves in the in- 

 terior of the earth as it does at the surface, 

 rocks similar to those in the earth's crust 

 can not extend to a depth of more than 

 forty-five miles below the surface. 



It is remarkable that Professor Milne 

 from the study of earthquake phenomena 

 had previously come to the conclusion that 

 rocks similar to those at the earth 's surface 

 only descend a short distance below the 

 siirface; he estimates this distance at 

 about thirty miles, and concludes that at a 

 depth greater than this the earth is fairly 

 homogeneous. Though the discovery of 

 radioactivity has taken away one method 

 of calculating the age of the earth it has 

 supplied another. 



The gas helium is given out by radio- 

 active bodies, and since, except in beryls, 

 it is not found in minerals which do not 

 contain radioactive elements, it is probable 

 that all the helium in these minerals has 

 come from these elements. In the case of 

 a mineral containing uranium, the parent 

 of radium in radioactive equilibrium, with 

 radium and its products, helium will be 

 produced at a definite rate. Helium, how- 

 ever, unlike the radioactive elements, is 

 permanent and accumulates in the min- 

 eral; hence if we measure the amount of 

 helium in a sample of rock and the amount 

 produced by the sample in one year we can 

 find the length of time the helium has been 

 accumulating, and hence the age of the 



rock. This method, which is due to Pro- 

 fessor Strutt, may lead to determinations 

 not merely of the average age of the crust 

 of the earth, but of the ages of particular 

 rocks and the date at which the various 

 strata were deposited ; he has, for example, 

 shown in this way that a specimen of the 

 mineral thorianite must be more than 240 

 million years old. 



The physiological and medical properties 

 of the rays emitted by radium is a field of 

 research in Avhich enough has already been 

 done to justify the hope that it may lead 

 to considerable alleviation of human suffer- 

 ing. It seems quite definitely established 

 that for some diseases, notably rodent 

 ulcer, treatment with these rays has pro- 

 duced remarkable cures; it is imperative, 

 lest we should be passing over a means of 

 saving life and health, that the subject 

 should be investigated in a much more sys- 

 tematic and extensive manner than there 

 has yet been either time or material for. 

 Radium is, however, so costly that few 

 hospitals could afford to undertake pion- 

 eering work of this kind ; fortunately, how- 

 ever, through the generosity of Sir Ernest 

 Cassel and Lord Iveagh a Radium Insti- 

 tute, under the patronage of his Majesty 

 the King, has been founded in London for 

 the study of the medical properties of 

 radium, and for the treatment of patients 

 suffering from diseases for which radium 

 is beneficial. 



The new discoveries made in physics in 

 the last few years, and the ideas and poten- 

 tialities suggested by them, have had an 

 effect upon the workers in that subject akin 

 to that produced in literature by the 

 Renaissance. Enthusiasm has been quick- 

 ened, and there is a hopeful, youthful, per- 

 haps exuberant, spirit abroad which leads 

 men to make with confidence experiments 

 which would have been thought fantastic 

 twenty years ago. It has quite dispelled 



