July 12, 1901.] 



SCIENCE 



57 



these are of the least peuetratiug kind, 

 which, according to the charged-particle 

 hypothesis, should, on the contrary, be 

 most deflected by the field. A satisfactory 

 hypothesis as to the nature of these non- 

 deflectable, non-penetrating radiations has 

 not yet been put forth. Perhaps they con- 

 sist of particles of much larger mass than 

 those of the deflectable rays. M. Villard 

 finds also in the radium radiations a small 

 proportion of very penetrating, non-deflect- 

 able raj^s, quite similar to the X-rays. 



ELECTROSTATIC EFFECTS. 



Now a stream of charged particles de- 

 flectable by a magnetic field should also be 

 deflected by an electrostatic field. This is 

 found to be the case. Furthermore, a 

 shower of negatively charged particles 

 ought to impart a negative charge to an in- 

 sulated conductor. Of course in this case 

 air would not act as an insulator, for it be- 

 comes a conductor under the action of the 

 rays. M. and Mme. Curie got around 

 this difSculty by insulating a conductor with 

 a thin layer of wax over its surface, then 

 exposed it to radium radiations and found 

 that it became highly charged negatively. 

 Insulating some of the radium salt in the 

 same manner with wax, they found that it 

 became highly chai'ged positively, a beauti- 

 ful corroboration of the theory that there is 

 a separation of the atomic particles with 

 their charges. If, as now seems almost 

 certain, the negatively charged part of the 

 atom has a mass only a small fraction, a 

 thousandth perhaps, of that of the positive 

 part, it is very reasonable that the negative 

 particles would be the ones to be shot out in 

 case of interatomic commotions. The rate 

 of charging in the experiment was about 4 x 

 10~^- amperes per sq. cm. of the radium salt. 



VELOCITY, MASS AND ENERGY OF THE 

 RADIATIONS. 



The velocity of a charged particle and 

 the ratio of the charge to the mass may be 



found by comparing its path in a magnetic 

 field with its path in an electrostatic field, 

 Then assuming the charged-particle hy- 

 pothesis it should be possible to calculate the 

 velocity of the particles in the deflectable 

 rays from the radio-active substances. 

 This has been done by M. Becquerel. The 

 curvature of the path in the magnetic field 

 can be measured without much difiiculty, 

 but the deflection in the electrostatic field 

 is very small. The difl&culty of the experi- 

 ment is also increased by the complex 

 character of the radiations, making it un- 

 certain if rays of just the same kind are be- 

 ing observed in the two fields. Some con- 

 fidence, however, must be placed in the re- 

 sults, though they give for the velocity of the 

 particles an astounding figure, about half 

 the velocity of light. How from a quiet, 

 peaceful bit of white salt particles can be 

 shot off with such a velocity as this remains 

 for explanation. The ratio of the charge 

 to the mass of the particles is of the same 

 order as in the case of the kathode rays, 

 another evidence that the atomic charges 

 are invariable and inseparably connected 

 with the particles. 



By measuring the rate at which a charge 

 is imparted to a conductor, and then using 

 the values of the A'^elocity and of the ratio 

 of the charge to the mass determined as 

 above, the kinetic energy per second of the 

 particles emitted may be calculated. For 

 a sq. cm. surface of a very active radium 

 preparation it has been found to be 5.1 ergs 

 per second, or five ten-millionths of a watt. 

 The mass of the particles, calculated from 

 the same data, is exceedingly small, the 

 loss from a sq. cm. of surface being some- 

 thing like a milligram in a thousand mil- 

 lion years. M. Becquerel observes that it 

 is of the same order as the evaporation of 

 certain odorous bodies. 



Professor Eutherford and Mr. McClung 

 made last year some interesting experiments 

 on the energy required to produce ionization 



