Absorption- Spectrum of Potassium Vapour. 



199 



No. Wave-length. 



1 G412 



2 6442 



3 6473 



4 6512 



5 6543 



6 6581 



7 6621 



These are what appear on the negative as quite definite 

 bands. There are outside these limits places which might be 

 edges but which are not definite enough and so have not been 

 included in this table. The measurements are accurate 

 within two or three units, and we may note in passing that 

 differences between neighbouring edges are approximately 30 

 and 40 units. Doubtful edges at 6383, 6353, give the same 

 differences, but no stress is laid on this point at present. 



In the case of sodium we have for the wave-lengths of 

 edges of the bands : — ■ 



4783 

 4810 

 4819 

 48:57 

 4866 

 4895 

 49:52 

 4962 

 4979 



5002 

 5041 

 5048 

 5080 

 5087 

 5119 

 5126 

 51.34 



These numbers are taken from Wood's paper in the Phil. 

 Mag. xii. 1906, p. 499. 



If now we tabulate the ratios of the wave-lengths of these 

 edges to the first member of the principal series for the two 

 cases, i. e. for sodium D 5896, for potassium 7699, we obtain 



the following numbers : — 



>tassium. 



Sodium 





•S112 





•8158 





•8174 





•8204 





•8252 



8328 



•8301 



•8367 



•8366 



•8408 



841 7 



■S460 



•S445 



•8499 



•8483 



•8548 



•8549 



8G02 



•8562 





•S615 





•«628 





•86S2 





•8694 





•8707 



