998 



SCIENCE. 



[N. S. Vol. XVII. No. 443. 



Faraday, in 1862, long and ardently 

 sought for a visible relation between mag- 

 netism and light which in 1845 he had 

 foreshadowed. But his instrumental means 

 were too feeble, and it was not till 1896 

 that Zeeman showed a spectrum line couhi 

 be acted on by a magneic field. A spec- 

 trum line is caused by motion of the elec- 

 tron. A magnetic field resolves this mo- 

 tion into other component motions, some 

 slower, others quicker, and thus causes a 

 single line to split into others of greater 

 and less refr.angibility than the parent 

 line. 



One important advance in theoretic 

 knowledge has been obtained by Dewar, 

 the successor of Faraday in the classic labo- 

 ratories of the Royal Institution. Soon 

 after Rontgen's discovery Dewar found 

 that the relative opacity to the Rontgen 

 rays was in proportion to the atomic 

 weights of bodies, and he was the first to 

 apply this principle to settling a debated 

 point in connection with argon. Argon is 

 relatively more opaque to the Rontgen rays 

 than either oxygen, nitrogen or sodium, 

 and from this Dewar inferred that the 

 atomic weight of argon was twice its 

 density relative to hydrogen. In the light 

 of to-day's researches on the constitution 

 of atoms, it is impossible to overestimate 

 the importance of this discovery. 



In 1896 Becquerel, pursuing the mas- 

 terly work on phosphorescence inaugurated 

 by his illustrious father, showed that the 

 salts of uranium constantly emit emana- 

 tions which have the power of penetrating 

 opaque substances and of affecting a pho- 

 tographic plate in total darkness, and of 

 discharging an electrometer. In some re- 

 spects these emanations, known as Becqu- 

 erel rays, behave like rays of light, but 

 they also resemble Rontgen rays. Their 

 real character has only recently been as- 

 certained, and even now there is much that 



is obscure and provisional in the explana- 

 tion of their constitution and action. 



Following closely upon Becquerel's work 

 came the brilliant researches of M. and 

 Mme. Curie, on the radio-activity of bodies 

 accompanying uranium. 



Hitherto have been recounting isolated 

 instances of scientific speculation with ap- 

 parently little relation to one another. The 

 existence of matter in an ultra-gaseous 

 state; material particles smaller than 

 atoms; the existence of electrical atoms or 

 electrons ; the constitution of Rontgen rays 

 and their passage through opaque bodies; 

 the emanations from uranium ; the disso- 

 ciation of the elements— all these isolated 

 hypotheses are now focused and welded 

 into one harmonious theory by the discov- 

 ery of radium. 



" Often do the spirits 

 Of great events stride on before the events, 

 And in to-day already walks to-morrow." 



No new discovery is ever made without 

 its influence ramifying in all directions and 

 explaining much that before had been 

 mystifying. Certainly no discovery of 

 modern times has had such wide-embracing 

 consequences, and thrown such a flood of 

 light on broad regions of hitherto inex- 

 plicable phenomena, as this discovery of 

 M. and Mme. Curie and M. Bemont, who 

 patiently and laboriously plodded along a 

 road bristling with difficulties almost in- 

 superable to others who, like myself, have 

 toiled in similar labyrinths of research. 

 The crowning point of these labors is ra- 

 dium. 



Let me briefly recount some of the prop- 

 erties of radium, and show how it reduces 

 speculations and dreams, apparently im- 

 possible of proof, to a concrete form. 



Radium is a metal of the calcium, stron- 

 tium and barium group. Its atomic weight 

 according to C. Runge and J. Precht is 

 probably about 258. In this case it occu- 

 pies the third place below barium in my 



