﻿548 Mr. D. Coster on the Spectra of X-rays 



the anticathode the radiation can be directed on any desired 

 part of the crystal. This change of the position of the 

 anticathode spot was easily obtained by a change of the rela- 

 tive position of the anticathode and the hot-wire cathode. 

 The hot wire must be renewed about every 8 hour^, and 

 frequently after this operation it was necessary to readjust 

 for the most favourable conditions of reflexion. 



The tension on the tube was about 25 k.v., the current 

 was not more than 15 m.a., the time of exposure varying 

 from 10 to 45 minutes. Calcite was used as analysing 

 crystal. Some trouble was caused by the copper K lines 

 and the tungsten L lines, which cannot be avoided when 

 working with a tube of brass and a tungsten hot wire. In 

 a few cases these foreign lines made it impossible to measure 

 some weak lines belonging to the element under inves- 

 tigation. 



§ 3. As regards the accuracy of the measurements I may 

 refer to Part II. § 4 of this paper. In general, the lines for 

 the elements La-Lu are much sharper than those for the 

 elements with lower atomic number. On the other hand, 

 most of the stronger lines are accompanied by fairly intense 

 satellites which often lie very close to them, thus diminishing 

 the accuracy of the measurements. Usually the errors in 

 the wave-lengths of the satellites themselves are larger than 

 those in the wave-lengths of the diagram-lines, as the satel- 

 lites are more diffuse. 



. With the exception of the lines j3 7 and y 8l which are dealt 

 with in Part IV. § 10, all the diagram-lines (see diagram IV. 

 Part V. § 2) are given in Tables XIII., XIV., and XV. 

 The lines appearing with two decimal places have been taken 

 from Hjalmar's precision measurements *, the other lines 

 having been determined in the present investigation relatively 

 to these lines or to the copper, tungsten, or zinc lines, which 

 also appeared on the plates. For the elements Eu, Gd, and 

 Tb the line r) could not be separated from a. x or a 2 , which are 

 much sharper and more intense. 



Zeitschr.f. Physik, iii. p. 262 (1920) and vii. p. 341 (1921). 



