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SCIENCE. 



IN. «. Vol. XVII. No. 443. 



the first time Rutherford has measured 

 their speed and mass, and he shows they 

 are ions of matter moving with a speed of 

 the order of that of light. 



There is also a third kind of emanation 

 produced by radium. Besides the highly 

 penetrating rays deflected by a magnet, 

 there are very penetrating rays not at all 

 affected by magnetism. These accompany 

 the previous emanations, and are Rontgen 

 rays— ether vibrations— produced as sec- 

 ondary phenomena by the sudden arrest 

 of velocity of the electrons by solid matter, 

 producing a series of Stokesian 'pulses' or 

 explosive ether waves shot into space. 



Many lines of argument and research 

 tending towards the same point give trust- 

 worthy data by which to calculate the 

 masses and velocities of these different 

 particles. I must deal with big figures, 

 but big and little are relative, and are only 

 of importance in relation to the limitations 

 of our senses. I will take as the standard 

 the atom of hydrogen gas— the smallest 

 material body hitherto recognized. The 

 mass of an electron is l/700th of an atom 

 of hydrogen, or 3 X 10""^" grm., accord- 

 ing to J. J. Thomson, and its velocity is 

 2 X 10"* centimeters per second, or two 

 thirds that of light The kinetic energy 

 per milligram is 10^' ergs, about three and 

 a half million foot-tons. Becquerel has 

 calculated that one square centimeter of 

 radio-active surface would radiate into 

 space one gram of matter in one billion 

 years. 



The positively electrified masses or ions 

 are enormously great in comparison with 

 the size of the electron. Sir Oliver Lodge 

 illustrates it thus: If we imagine an or- 

 dinary sized church to be an atom of 

 hydrogen, the electrons constituting it will 

 be represented by about 700 grains of sand 

 each the size of an ordinary full-stop (350 

 positive and 350 negative) dashing in all 



directions inside, or, according to Lord 

 Kelvin, rotating with inconceivable ve- 

 locity. Put in another way; the sun's 

 diameter is about one and a half million 

 kilometers, and that of the smallest plane- 

 toid about 24 kilometers. If an atom of 

 hydrogen be magnified to the size of the 

 sun, an electron will be about two-thirds 

 the diameter of the planetoid. 



The extreme minuteness and sparseness 

 of the electrons in the atom account for 

 their penetration. While the more mas- 

 sive ions are stopped by intercoUisions in 

 passing among atoms, so that they are 

 almost completely arrested by the thinnest 

 sheet of matter, electrons will pass almost 

 unobstructed through ordinary opaque 

 bodies. 



The action of these emanations on phos- 

 phorescent screens is different. The elec- 

 trons strongly affect a screen of barium 

 platinocyanide, but only slightly one of 

 Sidot's zinc sulphide. On the other hand, 

 the heavy, massive, non-deflectable positive 

 ions affect the zinc sulphide screen strongly, 

 and the barium platinocyanide screen in a 

 much less degree. 



Both Rontgen rays and electrons act on 

 a photographic plate and produce images 

 of metal and other substances enclosed in 

 wood and leather, and throw shadows of 

 bodies on a barium platinocyanide screen. 

 Electrons are much less penetrating than 

 Rontgen rays, and will not, for instance, 

 show easily the bones of the hand. A 

 photograph of a closed case of instruments 

 is taken by radium emanations in three 

 days, and by Rontgen rays in three min- 

 utes. The resemblance between the two 

 pictures is slight, and the differences great. 



The power with which radium emana- 

 tions are endowed of discharging electri- 

 fled bodies is due to the ionization of the 

 gas through which they pass. This can 

 be effected in many other ways; thus. 



