June 26, 1903.] 



SCIENCE. 



999 



lemniscate spiral scheme of the elements,* 

 two unoccupied gaps intervening. 



The spectrum of radium has several well- 

 defined lines; these I have photographed 

 and have also measured their wave-lengths. 

 Two especially are strong and character- 

 istic. One at wave-length 3,649.71 and 

 the other at wave-length 3,814.58. These 

 lines enable radium to be detected spectro- 

 seopically. 



The emanations cause soda-glass to as- 

 sume a violet color, and they produce many 

 chemical changes. Their physiological ac- 

 tion is strong, a few milligrams brought 

 near the skin in a few hours producing 

 a wound difficult to heal. 



The most striking property of radium 

 is its power to pour out torrents of emana- 

 tions bearing a certain resemblance to 

 Rontgen rays, but differing in important 

 points. 



The emanations from radium are of three 

 kinds. One set is the same as the cathode 

 stream, now identified with free electrons 

 — atoms of electricity projected into space 

 apart from gross matter— identical with 

 'matter in the fourth or ultragaseous 

 state,' Kelvin's 'satellites,' Thomson's 'cor- 

 puscles' or 'particles'; Lodge's 'disem- 

 bodied ionic charges, retaining individu- 

 ality and identity.' These electrons are 

 neither ether-waves nor a form of energy, 

 but substances possessing inertia (probably 

 electric). Liberated electrons are exceed- 

 ingly penetrating. They will discharge an 

 electroscope when the radium is ten feet 

 or more away, and will affect a photo- 

 graphic plate through five or six milli- 

 meters of lead and several inches of wood 

 or aluminium. They are not readily fil- 

 tered out by cotton-wool; they do not be- 

 have as a gas, i. e., they have not proper- 

 ties dependent on intercollisions, mean free 

 path, etc. ; they act more like a fog or mist, 



* Proc. Roy Soc, Vol. LXIII., p. 408. 



are mobile and carried about by a current 

 of air to which they give temporary con- 

 ducting powers, clinging to positively elec- 

 trified bodies and thereby losing mobility, 

 and diffusing on the walls of the contain- 

 ing vessel if left quiet. 



Electrons are deviable in a magnetic 

 field. They are shot from radium with a 

 velocity of about one tenth that of light, 

 but are gradually obstructed by collisions 

 with air atoms, so that some become much 

 slowed, and then are what I formerly called 

 loose and erratic particles, which diffuse 

 about in the air, and give it temporary 

 conducting powers. These can turn corn- 

 ers, can be concentrated by mica cones into 

 a bundle and then produce phosphores- 

 cence. 



Another set of emanations from radium 

 are not affected by an ordinarily powerful 

 magnetic field, and are incapable even of 

 passing through thin material obstructions. 

 These emanations have about one thousand 

 times the energy of those radiated by the 

 deflectable particles. They render air a 

 conductor and act strongly on a photo- 

 graphic plate. Their mass is enormous in 

 comparison with that of the electrons, and 

 their velocity is probably as great when 

 they leave the radium, but, in consequence 

 of their greater mass, they are less deflected 

 by the magnet, are easily obstructed by 

 obstacles, and are sooner brought to rest 

 by collisions with air atoms. The Hon. 

 R. B. Strutt* was the first to affinn that 

 these non-deflectable rays are the positive 

 ions moving in a stream from the radio- 

 active body. 



Rutherford has shown that these emana- 

 tions are slightly affected in a very power- 

 ful magnetic field, but in an opposite direc- 

 tion to the negative electrons. They are 

 therefore proved to be positively charged 

 bodies moving with great velocity. For 



*PhU. Trans. R. S., A, 1901, Vol. CXCVI., p. 



