404 Dr. M. Siegbahn and Mr. E. Friman on the 



<-> 



high frequency spectra, has shown that between aluminium 

 and gold only three elements, hitherto not detected, are to 

 be expected. 



This investigation aims at a determination o£ the elements 

 between gold and. uranium. Some temporary measurements 

 in this region have already been made by de Broglie* after 

 the secondary radiation method. A research of: lead also has 

 been made by Rutherford and Andrade t, using the 7 rays 

 from an emanation-tube as primary radiation. 



As in this case, however, a relatively large gap (of 

 6 elements) is to be passed over, measurements much more 

 accurate than those oE de Broglie are necessary. Our plates 

 of the X-ray spectra, therefore, are taken by the primary 

 radiation method, that i-, the element in question was placed 

 as anticathode in an X-ray tube. As, further, the wave- 

 length space under examination, the a-lines of the L-series, 

 consists of slightly absorbable rays, the tube was furnished 

 with a window of 0*05 mm. of aluminium. 



In this first research we have only determined one line for 

 every element, and this the strongest of the two a-lines of 

 the L-series. This group also is the best known of the four 

 forming the L-series in Moseley's research. His investi- 

 gation extended from zirconium to gold. By this research 

 the measurements thus are extended over more than 50 

 elements. 



2. In the spectrometric investigation a rotating rock-salt 

 crystal was used, the rotatory speed of which was about 1° in 

 4 min. Thereby every space was gone over several times 

 (between 4 and 16) according to the intensity of the rays. 

 As diaphragms (collimator) two lead slits were used, the first 

 with a width of 0*1 or 0'2 mm., the second of 1-2 mm. The 

 distances first slit-crystal and crystal-plate were equal (about 

 13 cm.). 



Of the elements examined, gold as thin sheet was soldered 

 on the copper anticathode, thallium, lead, and bismuth melted 

 on the tinned copper plate, mercury (as cinnabar), thorium 

 (as thorium oxide), and uranium (as metal powder) rubbed 

 on the copper plate, scratched with a rough file. 



The tube was evacuated with a molecular air-pump. 



3. The results of the measurements are given in the 

 following table : — 



* C. H. 1914. 



t Phil. Mag. [6] vol. xxvii. p. 851 (1914). 



