CONTEMPORARY ADVANCES IN PHYSICS 



351 



curve which I display as Fig. 3 is taken from the latest paper,' ^ but 

 the marked points comprise those of Lawrence's first article (large 

 circles) and those obtained in the interim by R. C. Williamson. '- The 

 monochromators used in these late researches gave narrower wave- 



POTASSIUM 



2200 



2400 



2600 

 ANGSTROMS 



2800 



3000 



Fig. 3 — Ionization by light plotted as function of wavelength for potassium 

 (Critical wavelength: 2856A). Circlets, crosses and large circles correspond to 

 different sets of observations by Lawrence & Edlefsen, Williamson & Lawrence. 

 (E. O. Lawrence, N. Edlefsen.) 



length-bands than those used formerly, and so revealed the small peak 

 at the proper limiting-frequency which had eluded Lawrence at the 

 outset. The much more prominent peak at shorter waves remains 

 outstanding. The data, be it mentioned, are here reduced to equal 

 intensities of light for the various wavelengths. 



11 Lawrence & Edlefsen, Phys. Rev., (2) 34, pp. 1056-1060 (1929). 

 i2Proc. Nat. Acad. Set., 14, pp. 793-799 (1928). 



