478 Scientific Intelligence. 



order spectrum of the more intense image. These bands are pro- 

 duced by very penetrating radiations which play the most 

 important part in X-ray phenomena when the total emission is 

 not minutely analyzed. They probably represent the electromag- 

 netic radiation caused by the sudden stopping of the cathode rays 

 by the anticathode. The rest of the spectrum consists of sharp, 

 discrete lines superposed on a much fainter, continuous back- 

 ground. By using an absorbing screen of glass l mm thick it was 

 found that the "lines " practically disappeared while the back- 

 ground was only weakened. This show's that the continuous 

 spectrum belongs to higher orders of the central bands. The 

 "lines" are similar to ordinary spectral lines, being single, mul- 

 tiple, sharp, diffuse, strong, weak, etc. For details of wave- 

 lengths, dispersive power of various crystals, and many other 

 important data reference must be made to the original article. — 

 Jour, de Phys., vol. iv, Feb., 1914, p. 101. h. s. u. 



7. Removal of the Photoelectric Effect of Potassium. — In the 

 March number of this Journal attention was called to the experi- 

 mental work of Ktistner in which the photoelectric effect of zinc 

 was entirely suppressed. This very important result confirms the 

 hypotheses advanced several years ago by W. Hallwachs as well 

 as the theoretical considerations and experimental facts recently 

 published by this investigator in collaboration with G. Wieclmann. 

 (The earlier work happened to appear in print after the later.. 

 The priority seems to belong to Hallwachs and Wiedmann rather 

 than to Fredenhagen and Ktistner.) 



Starting with the idea that the photoelectric effect exhibited 

 by metals could be suppressed by removing the last traces of 

 gases, Hallwachs and Wiedmann investigated potassium and 

 hydrogen, since the alkali metals give the strongest effect, since 

 potassium is always used in photoelectric cells, since hydrogen is 

 usually present in such cells, and since potassium absorbs hydro- 

 gen in remarkably large quantities. (One volume of potassium 

 absorbs 126 volumes of hydrogen.) In other words, if it could 

 be shown that potassium, which initially contained a great deal 

 of hj'drogen, could have its photoelectric properties destroyed by 

 freeing it completely from this gas, the result would afford the 

 strongest evidence in favor of the hypothesis that the presence of 

 a gas is a necessary condition for the existence of the photoelec- 

 tric effect in metals. The apparatus used was of too complicated 

 a design to admit of easy description without the aid of a 

 diagram. Suffice it to say that five glass bulbs were so arranged 

 as lateral branches of a long evacuating tube as to enable the 

 experimenter (Wiedmann) to distil with extreme slowness the 

 potassium from one bulb to the next in the series. Each bulb 

 could be sealed off at will and tested for its photoelectric effect 

 by comparison with a standard cell. The fourth bulb, which 

 contained thrice distilled potassium, gave about the same deflec- 

 tion before and after illumination. This was largely due to sur- 

 face conduction. After several days it was possible to suppress 



