October, 1903.] 



KNOWLEDGE. 



217 



Founded by RICHARD "A. PROCTOR. 



Vol. XXVI.] LONDON: OCTOBER, 1903. [No. 216. 



CONTENTS. 



Radium. By Edwin Edser, a.e.c.sc, f.ph.s. 



Mans Place in the Universe. By E. Walter M.mtndbb, 



r.B.A.s. ... 

 The Claws on the Wings of Birds : A Study In 



Evolution. By W. P. Pycbatt, a.l.3., f.z.s , etc. ... 

 Cycles of Eclipses. By A. C. D. Crommelin. (Illustrated) 

 The Chemistry of the Stars. V. — The Orion Stars. 



By A. Fowler, f.r.a.s. (Illustrated) 

 The Sun as Photographed on the K-Line. (Illustrated) 

 Photograph of the Sun in " K. Light," showing 



Calcium Clouds. (Plate.) 

 Letters : 



Boreelly's Comet, 1903. By R. C. Johnson (Illus.) 



Curious Sunset Puenomenon. By E. E. Mabkwick, Col. 



Method OF AscEBTAiNiNa Moon's AsE. By Edwin Holmes 



Notes 



British Ornithological Notes. Conducted by Habet F. 



WiTHBHBT, F.Z.8., M.B.O.U. ... 



Notices of Books 



Books Received 

 TIrerrill and Drumahair. By Geenville A. J. 



M.B.r.A., F.O.S. ... 



Microscopy. Conducted by M. I. Cboss 



Xl'MEBICAL ApEETUEE AND RAPIDITY. By 



CoNRADY, E.E A.S., F.E M.S. 



FbeshWatek Mites. By Chas. D. Soae, f.b.m.s. 

 Notes on Comets and Meteors. By W. F. Dknnino, 



r.B.A.s. ... ... ... ... ... ... 



The Face of the Sky for October. By W. Shacklbton, 



F.B.A.B. (Illustrated) 



Chess Column. By C. D. Looock, b.a 



Cole, 



A. E. 



PAGE 



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233 

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235 

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236 

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239 

 240 



RADIUM. 



By Edwim Edsek, a r.c.Sc, f.ph.s. 



Many and various are the effects, apparent in the present 

 aspect of science, which may be traced to Prof. Riintgen's 

 classical discovery of " X-Rays " in 1895 ; of these, not 

 the least important is the sustained interest manifested in 

 connection with all problems relating to radiation. To 

 this interest must be ascribed the Itrilliant series of 

 researches which have cubniuat«d, for tlie time being, in 

 the discovery of a new element. Radium ; an element 

 possessing properties so far removed from thosi' generally 

 imputed to matter, that many of our aeceptiMl soientitie 

 theories are found to ivcjuire reconsideration, wliile some 

 must be profoundly modified or even abandoned. A 

 characteristic continually recurring in these researches is 

 the unexpectedness of tlie results achieved; o^er and over 

 again an experimenter, when seeking for some effect which 

 might rationally have been anticipated, has come across a 

 phenomenon which may fairly be said to have transceuded 

 all previous knowledge. 



A beginning was made in 1896 by M. Henry, who 



showed that phosphorescent sulphide of zinc emits radia- 

 tions which can penetrate lilack paper, and affect a photo- 

 graphic plate. About the same time M. Niewenglowski 

 found that sulphide of calcium, rendered phosphore.=cent 

 by exposure to sunlight, emits radiations which can pene- 

 trate a thin sheet of aluminium. Unlike X-rays, these 

 radiations are refracted by glass ; they apparently con- 

 stitute an intermediate link between ordinary ultra-violet 

 hght and X-rays. M. Henri Becquerel followed up these 

 researches by placing various phosphorescent substances 

 above photographic plates shielded from light by layers of 

 black paper or aluminium. On one occasion a plate was 

 enclosed in black paper, on the outside surface of which a 

 quantity of the double sulphate of uranium and potassium 

 was sprinkled. It had been intended to expose this 

 arrangement to sunlight in order to provoke phosphores- 

 cence in the uranium salt, but the weather proving 

 inclement, the prepared plate was placed just as it was in 

 a drawer, where it was left for several days. By a lucky 

 chance it was afterwards decided to develop this plate ; 

 on doing so, it was found that it had Ijeen affected by 

 some form of radiation emitted by the uranium salt, 

 although the latter, having remained unexposed to sun- 

 light, had produced no visible phosphorescence. Subse- 

 quent experiments showed that the uranium salt appa- 

 rently possessed the property of continually emitting radia- 

 tions, which, though invisible to the eye, could traverse 

 paper, wood, or aluminium, and subsequently decompose 

 silver salts. It was found that this property persisted, 

 without any discernible falling oft', after three years, during 

 the whole of which time the active substance was enclosed 

 in a leaden box with double walls. These radiations were 

 termed "Becquerel rays," in honour of their discoverer. 

 It was at first thought that they were extinguished by 

 crossed tourmalines, in which case we should have had to 

 conclude that they were polarizable, and therefore essen- 

 tially transverse ether vibrations resembling ordinary 

 light, but differing from it, in all probability, in having 

 a much smaller wave-length. Subsequent experiments 

 proved, however, that there was no conclusive evidence of 

 polarization. 



Becquerel's discovery excited considerable attention, and 

 much surprise was naturally evinced that any substance 

 should be capable of continually emitting energy without 

 showing signs of ultimate exhaustion. Had we at last 

 found a case to which the law of conservation of energy 

 did not aiiplyV Could we be said to have found au 

 inexhaustible source of energy ? These questions were 

 frequently asked. But to be fruitful, such questions must 

 be submitted to nature, and not merely propounded in 

 newspapers or the pages of a scientific periodical. Among 

 those who felt themselves impelled to seek further ex- 

 perimental evidence on this interesting topic must be 

 mentioned M. Pierre Curie and Mine. Sklodowska Curie. 

 To understand the advance these iuvestigat^jrs effected, it 

 must be nieutioued that the radiations emitted by uranium 

 salts are very feebU", reijuiriiig many hours even to affect 

 a photographic plate. The metal uranium was discovered 

 in 1789 by the German chemist Klaproth ; it has anatomic 

 weight of 239, and occurs in various minerals, notably 

 " urauinite " or " pitolibleude." which is a mineral con- 

 taining about 81'5 per cent, of uranium, -i per cent, of 

 lead, and 5 per cent, of iron, with oxygen, water, and 

 various impurities. It occurred to Mine. Curie to test the 

 radio-activity of the residue obtained after removing the 

 uranium from pitchblende. To her surprise, she found 

 that the radio-activity of the i-esidue was far greater than 

 that of the sepamted uranium salt. The radio-activity 

 observed by Becquerel was thus proved to be due to some 

 hitherto unknown substance or substances occurring in 



