282 v Scientific Intelligence. 



As a consequence of previous work, by various experimenters, 

 on the absorption of /3-rays coming from the radium family, it 

 was expected that three groups of bands, pertaining respectively 

 to Ra, RaB, and RaC, would be found in the magnetic spectrum. 

 A photographic negative obtained with the active deposit of 

 radium, when a field of about 107*5 gauss was used, showed 9 

 bands for the /3-rays in addition to the single stripe which was 

 produced by the practically undeviated a-rays. On another nega- 

 tive, corresponding to a field of 215 gauss, it was possible to 

 measure the magnetic linear dispersion of 7 /3-ray stripes or bands. 

 The greatest deviation was, in this case, about 5 mrn . The nega- 

 tive is reproduced in the paper and most of the bands show quite 

 distinctly. By appropriate, and rather obvious methods, the 

 authors identified the rays which pertain to radium B and C 

 respectively (both of these "elements" being present in the active 

 deposit). For radium C there were four discrete pencils of /3-rays 

 having speeds of 98, 94, 86, and 80 per cent of the velocity of 

 light. Radium B was associated with the following speeds : 

 74, 69, 63, 41, and 36 per cent of 3X10 10 cm/sec. Lastly, the 

 magnetic spectrum of radium itself was investigated. The repro- 

 duction of the negative shows two well-separated stripes corre- 

 sponding approximately to speeds of 65 and 52 per cent of the 

 velocity of light. In conclusion it may be remarked that additional 

 interest attaches to this series of experiments because in the earlier 

 investigations of Kauf mann, Bucherer, and others the discontinuity 

 of the magnetic spectrum had not been detected. — Physikal. 

 Ztschr., Dec. 1, 1911. h. s. it. 



9. The Production of Characteristic Rdntgen Radiations. — In 

 an earlier paper R. Whiddington gave a detailed account of his 

 investigation of the production and properties of soft Rontgen 

 radiation (Proc. Roy. Soc, vol. lxxxv, pp. 99-118). He has since 

 extended his research on X-rays to the chief properties of charac- 

 teristic radiations. These properties may be stated as follows : 

 (a) It is only when the primary rays contain a constituent more 

 penetrating than the characteristic to be excited that the stimu- 

 lation can be effected, (b) The penetrating power of a charac- 

 teristic radiation increases with the atomic weight of the emitting 

 element. (The adjectives " homogeneous" and "fluorescent" are 

 often used, in this connection, in place of " characteristic") The 

 experiments described define the quality of the softest primary 

 radiation which can stimulate a characteristic, in terms of the 

 speed of the cathode rays within the exciting X-ray tube. 



Certain parts of the apparatus used merit a brief description. 

 The cathode rays were produced in a discharge tube which was 

 fitted with a special hardening device (loc. cit.). By this means the 

 speed of the cathode rays could be instantly changed to almost 

 any desired value without altering the gas pressure. The cathode 

 rays were admitted through a horizontal, radial tube into a brass 

 cylinder whose axis of revolution was horizontal. The outside of 

 this cylinder was wound with a solenoid so that a uniform mag- 



