August 9, 1906] 



NA 'JURE 



557 



livu. He was elected a Fellow of the Royal Society in 

 1S78, and resided in this country during the remaining 

 vpars of his life. 



The death of Charles Jasper Joly, F.R.S., at the early 

 age of forty-one, robbed mathematics and astronomy of one 

 of their most devoted disciples. His " Manual of 

 Quaternions " is well known, and those acquainted with 

 his astronomical work are confident that, had his life been 

 spared, he would, as .\stronomer Royal of Ireland, have 

 added lustre to an office held by many distinguished prc- 

 iliM'essors. 



Samuel Pierpont I-angley was born in 1834. In 1866 

 ho became Director of the Alleghany Observatory at Pitts- 

 burg. His first work was the institution of a uniform 

 system of time froin the Atlantic seaboard to the Great 

 f^ikes. This, the first successful attempt to introduce 

 uniformity of time over a large area, was subsequently 

 widely imitated. In 1880 he invented the bolometer, and 

 thus opened out a large new field of investigation into the 

 invisible rays of long wave-length proceeding from heated 

 bodies. He analysed in minute detail the lunar heat spec- 

 trum, and, more recently, he conducted an inquiry into 

 ihc nature of the radiations emitted by the glow-worm. 

 In 1881 he conducted his researches into the solar heat 

 iif the earth's atmosphere. In 18S7 he became Secretary 

 to the Smithsonian Institution. The result of twenty years' 

 labour is to be found in the accurate determination, by 

 temperature alone, of more than seven hundred lines in 

 the invisible red spectrum, lines which are fixed with an 

 average probable error of about one second of arc. In 189 1 I 

 he published his experiments in aerodynamics, in 1893 I 

 " The Internal Work of the Wind," and in 1896 he 1 

 demonstrated by actual experiment that a body nearly a 

 thousand times heavier than air can be driven through 

 and sustained by it. His published works show great 

 literary charm. He especially excelled in the presentation 

 iif abstruse subjects in simple and non-technical language. 

 This is, perhaps, hardly the occasion to refer to his social 

 qualities. Those who had the privilege of his acquaint- 

 ance, however, can best testify to his quickness of insight, 

 his intense sympathy, especially with the young, and the 

 impression of capability which he produced upon all with 

 \vhoni he came in contact. 



The tragic death of Prof. Curie was felt as a calamity, 

 not only by those closely interested in the march of scien- 

 tific discovery, but also by those who had but a super- 

 ficial knowledge of his work. .\ teacher for more than 

 twenty years, he was nevertheless enabled by his enthusiasm 

 and energy to perform those researches which will ever be 

 connected with his name and that of his wife. So entirely 

 has public attention been attracted to their joint work on 

 the separation of the compounds of radium and their 

 properties that we are apt to overlook other great services 

 he rendered to science. His paper on " The Effect of 

 Temperature on the Magnetic Properties of Bodies " led 

 to the discovery of the law that for feebly magnetic sub- 

 stances the coefficient of magnetism varies inversely as the 

 absolute temperature. He also pointed out that the 

 magnetisation of diamagnetic substances appeared to be 

 independent of the temperature and physical state, in- 

 dicating diamagnetism as an atomic property. 



It is pleasing to reflect that the importance of his dis- 

 coveries received immediate recognition. It was but three 

 years before his death that he announced to the French 

 .\cademy the discovery of the new element, and in the same 

 vear he and Mme. Curie received the Daw Medal of the 

 Royal Society and the Nobel Prize ; and in July of last 

 year he was elected to the French .^cad^mie des Sciences. 

 He was one of the most modest and retiring of men, and 

 this honour 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 greativ 

 extended the domain of physics by the discovery of radio- 



A quarter of a century has passed since this Section, 

 meeting in this city of York, had the privilege of listen- 

 ing to a Presidential address by the pioneer of natural 

 knowledge whom we now know as Lord Kelvin, and it 

 mav possibly be a not unprofitable task to review briefly 



NO. I9I9. VOL. 74] 



a few of the advances which must render the interval a 

 memorable one in the annals of science. 



Lord Kelvin summarised the stores of energy from which 

 mechanical effects can be drawn by man as follows : — 



(i) The food of animals. 



(2) Natural heat. 



(3) Solid matter found in elevated positions. 



(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 radio- 

 activity have enormously increased our estiinate of the 

 stores of energy surrounding us, but so far these additional 

 stores cannot be regarded by us as stores froin which 

 " mechanical effects may bo drawn by inan." It is possible 

 that in the ingenious radium clock which we owe to Mr. 

 Strutt we have a source of mechanical energy unsuspected 

 in i88i, but, at all events, regarded from a commercial 

 standpoint, it can hardly be considered as " available by 

 man." Nevertheless, there is a sense in which it may bo 

 said that we are profiting by atomic energy, for we are 

 no longer bound to limit our estimate of the energy duo 

 to the radiant heat of the sun and the internal heat of the 

 earth by previously known dynamical considerations, and. 

 in consequence, our opinions with regard 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 con- 

 clusions 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 centimetre cannot much 

 exceed 1-75x10-" gram. The conclusions of Rutherford, 

 based on somewhat different values for the constants in- 

 volved, give an equivalent of 1-52x10-". Now Strutt has 

 found that the poorest igneous rock examined by him, 

 namely, Greenland 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, &c. 



We appear, therefore, to be driven to one of two assump- 

 tions : either (u) that the rate of heat production by radium 

 diminishes as we approach the centre of the earth ; or (b) 

 that the interior of the earth differs markedly in constitu- 

 tion from the exterior crust. 



It is true that Mr. Makower has shown that there is a 

 slight change of activity in one of the radium products 

 about the temperature of 1200° C, and it is very desirable 

 that this inquiry should be pushed to much higher limits. 

 At the same time, it appears evident that but a very slight 

 change in activity takes place at temperatures below 

 1500° C. 



Now Mr. Strutt has shown, arguing from known data, 

 that the maximum temperature at the bottom of a crust 

 of about forty-five miles in thickness, must be in the neigh- 

 bourhood of 1530° C, although some amount of uncertainty 

 is necessarily induced by our want of knowledge of the 

 conductivity of rock at high temperatures. Anyhow, it is 

 probable that at the depth indicated the temperature does 

 not exceed the melting-point of platinum. Such a crust 

 would contain about one-thirtieth of the earth's volume, 

 and if throughout it the radium heat energy were of the 

 average of that exhibited by many samples examined by 

 Strutt, the temperature of the earth could be maintained 

 until our stores of uranium suffered sensible depletion. 

 Such an assumption would lead to the conclusion that the 

 whole of the central portion of the earth consists of non- 

 radio-active substances at an approximate uniform tempera- 

 ture somewhat below the melting-point of platinum. A 

 brief summary of the evidence previously at our disposal 

 may not be out of place. 



In the first edition (1867) of Thomson and Tait's 

 " Natural Philosophy " we find the tidal evidence sum- 

 marised as follows : " It seems certain, therefore, that the 



