128 



SCIENCE 



[N. S. Vol. XXXVII. No. 943 



of non-cleviability in a magnetic field. For 

 neither a- nor ;3-rays ever eject electrons 

 from the matter through which they pass 

 with ionizing speeds. The energy which 

 the X-ray or the y-ray imparts to its chosen 

 electron has been conclusively shown by 

 many observers to be altogether indepen- 

 dent of the intensity of the X-rays, and 

 also independent of the nature of the atom 

 from which the electron is hurled.^* It 

 depends solely upon the penetrating power, 

 or hardness, of the X-ray. In fact, there is 

 strong evidence now for the statement that 

 although only a thousandth part of the 

 energy of the cathode-ray beam in an X-ray 

 tube is transformed into X-rays at the 

 anticathode, yet when these same X-rays, 

 weak in energy as a whole, fall upon mat- 

 ter outside the tube, they eject electrons 

 from it with energies as great or nearly as 

 great as those of the individual electrons 

 of the original cathode rays.-^ It is as 

 though the same energy were passed on in 

 new form whenever an X-ray produces a 

 (8-ray, or a cathode-ray, an X-ray. These 

 facts seem to be completely inexplicable on 

 any sort of a spreading wave theory. The 

 assumption of a continuous absorption by 

 an atom of X-ray energy until the atom 

 accumulates a sufficient store to eject an 

 electron with the observed speed is com- 

 pletely untenable, for the time required for 

 it to do this, according to the spreading 

 pulse theory, would be longer than the life 

 •of any X-ray bulb, yet as a matter of fact 

 this ejection begins the instant the X-ray 

 bulb is started. Precisely the same argu- 

 ment holds for y-rays. For these are found 

 to eject electrons from matter through 



'*Iimes, Proc. Boy. Soc, LXXIX., p. 442; Sad- 

 ler, Phil. Mag., March, 1910; Bestelmeyer, Ann. d. 

 Fhys., 22, 429. 



^ Bragg and Madsen, Phil. Mag., May and De- 

 cember, 1908 ; Whiddington, Proc. Boy. Soc, 1911 

 and 1912. 



which they pass with .9 the velocity of 

 light. This corresponds to an energy of 

 7 X 10"^ ergs. According to Rutherford, 

 the total energy of the y-rays per gram of 

 radium is 4.7 X 10"* ergs, and if we assume 

 that the number of y-ray pulses is the same 

 as the number of fi-rays emitted, namely, 

 7 X 10", then the whole energy in a y-ray 

 is very nearly 7 X 10"^" ergs, i. e., it is 

 precisely the same as the energy communi- 

 cated by the y-rays to the ejected electron 

 even though this ejection may happen at a 

 distance of 50 or 100 meters from the 

 source. There is then no escape from the 

 assumption in the case of X-rays, nor in the 

 case of y-rays, unless it be found in the 

 uncertainty of the assumption of the iden- 

 tity of the number of y-ray pulses and the 

 number of /?-raj^s, that the emitted energy 

 keeps together as an entity, or quantum, 

 which may be transformed back and forth 

 between a j8-ray and an X- or y-ray. This 

 energy is slowly dissipated into heat in its 

 passage through matter while it is in the 

 form of a yS-ray, but apparently not at all 

 while in the form of an X- or y-ray. This 

 argument is so close to the undeniable 

 experimental facts, at least as they now 

 stand, that if X- and y-rays stood by them- 

 selves it is probable that there would be 

 few opponents to Bragg 's theory as to the 

 corpuscular nature of these raj^s. His 

 actual assumption is that X- and y-rays 

 consist of neutral doublets whose velocity 

 determines the hardness of the ray. This 

 is an assumption the truth or falsity of 

 which could be tested if we could find the 

 speed of X-rays. Opinion is still divided, 

 however, as to the validity of conclusions 

 drawn from the attempts that have been 

 thus far made to identify the velocity of 

 X-rays with the velocity of light.-" Even 



«Marx, Ann. d. Phys., 33, p. 130.5, 1910, and 

 Franek and Pohl, Ann. d. Phys., 34, p. 936, 1911. 



