Knowledge. 



With which is incorporated Hardwicke's Science Gossip, and the Illustrated Scientific News. 



A Monthly Record of Science. 



Conducted by Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 



APRIL, 1915. 



CHAPTERS IN SPECTRUM ANALYSIS. 



By W. MARSHALL WATTS, D. Sc. 



I. — Law and Order in Spectra. 

 A. Line Spectra. 



(Continued from page 69.) 



The absorption spectra of potassium, rubidium, and 



caesium show long series of regularly arranged 



pairs of lines similar to those seen in sodium. 



These three metals are very closely allied in their 



chemical and physical properties, and their spectra 



show a most remarkable agreement. In the 



diagram (see Figure 79) these three spectra are 



mapped upon a scale of oscillation-frequency — 



that of caesium at a "height" of 17638, that of 



rubidium at the "height" of 7301, and that of 



potassium at the "height " of 1 528, as shown by the 



scale on the left-hand edge of the diagram, these 



numbers being the squares of the atomic weights : 



132-81 for caesium, 85-45 for rubidium, and 39-1 



for potassium. The connecting -lines, marked 



m = 2>, m=\, m=5, and so on, show the exact 



correspondence of the spectra line for line. Further, 



the lines joining corresponding points in caesium 



and potassium pass almost exactly through the 



corresponding points in rubidium. 



The principal series in potassium is set forth' in 



the following table, with the wave-lengths calculated 



from the formulae 



n it iconc u 109675 



O.F. = 35005-56 — nA , QCAxa 



'» + . 293076 -^?) 



m 



I 



for the less refrangible component, and 



109675 



O.F. = 35005-56 — 



m + -296228 - I^ 8 )' 



»i 



1 



for the more refrangible component of the pairs 

 of lines. 



Table 18. 

 The Principal Series in Potassium. 



97 



