SeJptembeb 21, 1906.] 



SCIENCE. 



355 



law that for feebly magnetic substances 

 the coefficient of magnetism varies inverse- 

 ly as the absolute temperature. He also 

 pointed out that the magnetization of dia- 

 magnetic substances appeared to be inde- 

 pendent of the temperature and physical 

 state, indicating diamagnetism as an atomic 

 property. 



It is pleasing to reflect that the impor- 

 tance of his discoveries received immediate 

 recognition. It was but three years before 

 his death that he announced to the French 

 Academy the discovery of the new element, 

 and in the same year he and Mme. Curie 

 received the Davy medal of the Royal So- 

 ciety and the Nobel prize ; and in July of 

 last year he was elected to the French 

 Academic des Sciences. He was one of the 

 most modest and retiring of men, and this 

 honor came to him unsought ; his name will 

 ever be remembered as one of the .most 

 notable of that brilliant band of workers 

 who have within recent years so greatly 

 extended the domain of physics by the dis- 

 covery radioactivity. 



A quarter of a century has passed since 

 this section, meeting in this city of York, 

 had the privilege of listening to a presiden- 

 tial address by the pioneer of natural 

 knowledge whom we now know as Lord 

 Kelvin, and it may possibly be a not un- 

 profitable task to review briefly a few of 

 the advances which must render the in- 

 terval a memorable one in the annals of 

 science. Lord Kelvin summarized the 

 stores of energy from which mechanical 

 efl'ects can be drawn by man as follows: 

 (1) the food of animals, (2) natural heat, 

 (3) solid matter found in elevated posi- 

 tions, (4) the natural motions of water and 

 air, (5) natural combustibles, (6) artificial 

 combustibles. 



The twenty-five years which have since 

 elapsed have not made it possible to extend 

 this list. It is true that within the last 



few years the discoveries connected with 

 radioactivity have enormously increased 

 our estimate of the stores of energy sur- 

 rounding us, but so far these additional 

 stores can not be regarded by us as stores 

 from which 'mechanical effects may be 

 drawn by man.' It is possible that in the 

 ingenious radium clock which we owe to 

 Mr. Strutt we have a source of mechanical 

 energy unsuspected in 1881, but, at all 

 events, regarded from a commercial stand- 

 point, it can hardly be considered as 'avail- 

 able by man.' Nevertheless, there is a 

 sense in which it may be said that we are 

 profiting by atomic energy, for we are no 

 longer bound to limit our estimate of the 

 energy due to the radiant heat of the sun 

 and the internal heat of the earth by pre- 

 viously known dynamical considerations, 

 and, in consequence, our opinions with re- 

 gard to the limit of the ages which the 

 physicist could allot to the evolutionist 

 have undergone profound modification. 



I here wish to draw attention to some of 

 the conclusions to which we are led by the 

 work of Mr. Strutt. 



Assuming the earth to be in thermal 

 equilibrium, then, even if the whole of this 

 interior heat be due to radium alone, the 

 mean quantity per cubic centimeter can 

 not much exceed 1.75 X 10"^^ gram. The 

 conclusions of Rutherford, based on some- 

 what different values for the constants 

 involved, give an equivalent of 1.52 X 10"^^. 

 Now Strutt has found that the poorest igne- 

 ous rock examined by him, namely, Green- 

 land basalt, contains more than ten times 

 this quantity, and an average rock fifty or 

 sixty times the amount. The assumption 

 that the earth is cooling only aggravates 

 the difficulty, and facts appear to tell 

 against the theory that it is getting hotter. 

 Also, we must take into consideration the 

 heat due to the existence of uranium, 

 thorium, etc. 



