1084 Mr. D. Coster on the Spectra of X-rays 



Hjalmar and Friman found ft, ft, and ft as far down 

 as Pd, Yi appears for the last time for Mo in their tables, 

 and the rj-l and Y 5 -ft doublets were not observed at all 

 in this region. But I could still detect ft and ft for Sr 

 and Rb, ft and j] were found as far down as Zr, although 

 very faint (Hjalmar's value of X= 5295'1 for Nbft corre- 

 sponds to my value of \= 5295*9 X.U. for ft for the same 

 element). The lines y 2i 73, and 7 4 in this region had not 

 been identified correctly by the former authors. The line 

 725 3 (72 an( i 7s could no longer be separated in this region) 

 has still been observed for Rb and 74 still for In. Both 

 doublets r]-l and 75-ft could also be measured down to 

 Rb and Sr. 



The spectra of the elements Ba and Cs were taken with a 

 rocksalt crystal, Te-Pd with calcite, Rh partly with calcite, 

 partly with gypsum, and Ru-Rb with a gypsum crystal. 

 For these elements the breadth of the lines was considerably 

 greater than the width of the slit, implying that the lines 

 represent a finite frequency interval. Strongly exposed 

 lines obtained with a rocksalt or calcite crystal, especially, 

 were diffuse at the edges, which obviously reduced the 

 accuracy of the measurements. Extremely broad and diffuse 

 were the lines, 7), I, and 72,3. For ft for some elements a 

 broadening could be observed at the short wave-length side. 

 The lines a x and ft were accompanied by satellites (see 

 Part II. § 7), while for the lightest elements # 2 could not 

 be separated from et lm All this reduced the accuracy of 

 the measurements. Usually only reference measurements 

 were made. The distance on the plate to the reference 

 line was often fairly large, sometimes over 10 mm., and in a 

 few cases even between 15 and 20 mm. Thus errors in 

 the measurements of the line-distances and irregularities 

 in the structure of the crystal may be quite appreciable 

 here. In the case of the lines taken with a rocksalt or 

 calcite crystal, however, the error in the wave-lengths must 

 be in nearly all cases considerably smaller than one X.U. 

 This is especially true of the lines lying in the neighbour- 

 hood of a reference line. In a few cases (sometimes for 77, 

 Z, and 72,3) this error may be a little larger. Some lines 

 could not be measured under a microscope and their distance 

 was estimated with a millimetre scale. They stand in the 

 tables without decimals in the wave-lengths. Their errors 

 may be more than 2 X.U. Using gypsum as analysing 

 crystal, we have on the one hand the disadvantage of the 

 greater space-lattice constant, on the other hand the ad- 

 vantage of getting sharper lines, which usually lie nearer 



