84 



Prof. F. Allen on the Persistence of 



that the brightest points of the spectra, represented by the 

 lowest values in the curves, gradually shift from the yellow 

 towards the blue as the spectral intensities grow smaller.. 



Fig. 2. 



The displacement of the brightest point here indicated is not 

 so great as other observers have obtained by different methods. 

 In fig. 3 the coordinates are the values of the luminosity, L, 

 and the wave-lengths in Table I. These give a correspondino- 

 series of luminosity curves for spectra of diminishing in- 

 tensities, the brightest spectrum being represented by the 

 highest curve. These are of the usual type of luminosity 

 curves, and also show the displacement of the brightest 

 point of the spectrum towards the blue when the intensities 



