5 



Prof. F. Allen on 



the Persistence 



of 











Table IT. 









( 



urves for Diminishing 



Intensity of Spectrum. 





Angle 

















between 



Pol. and 



Anal. 



7 * 



A=-72f 



fi. 



X=ffi5[i; 



\=-590 fi. 





D 



l 



D 



l 



D 



1 



a. 



cos 2 a. 





D 





I) 





D 



0° 



i-000 



•0286 sec. 



34-96 



•0184 sec. 



54-35 



•0153 sec. 



65-36- 



20° 



0-883 



•0290 



34-48 



•0187 



53-48 



•0155 



64-52 



40° 



•587 



•0312 



32-05 



•0198 



50-50 



•0162 



61-73 



60° 



•250 



•0366 



27-32 



0224 



44-64 



•0178 



5648 



70° 



•117 



•0436 



22-93 



•0251 



39-84 



•0196 



5102 



80° 



•030 



•0603 



16-58 



•0324 



30-86 



•0238 



42-02 



85° 



•0076 







•0454 



22-03 



•0303 



33 03 



87° 18' 



•0022 







•0625 



16-00 



•0366 



2732 



88° 12' 



•00098 







•0820 



12-19 



•0397 



25-19' 



88° 30' 



•00068 











0434 



23-04 







A = -520 



A__ 



n. 



X = -460/i. 



\ = -430ju. 



a. 



cos 2 a. 



J) 



1 

 D 



D 



1 

 I) 



D 



1 



0° 



1000 



•0169 sec. 



59-17 



•0254 sec. 



39-37 



•0448 sec. 



22-32 



20° 



0-883 



•0172 



57-55 



•0261 



38-31 



•0461 



21-69' 



40° 



•587 



•0182 



54-39 



•0279 



35-84 



•0507 



19-72 



60° 



•250 



•0202 



49-50 



•0317 



31-55 



0622 



16-08 



70° 



•117 



•0224 



44-64 



•0359 



27-86 



•0805 



12-42 



80° 



•030 



•0268 



37-31 



•0476 



21-00 



•0980 



10-20" 



85° 



•0076 



•0340 



29-41 



•0694 



14-41 



•0936 



1068 



87° 18' 



•0022 



•0415 



2409 



•0795 



12-58 







88° 12' 



•00098 



•0467 



21-41 











88° 30' 



•00068 















Fron] 



the Ferry-Port 



er law 



we have 



the relation 









1 

 IT 



= k\ogL + k'. 









By plotting the values of -=r and cos 2 « on semilogarithmic- 



paper, there results a group of straight lines which are shown 

 in fig. 4. Each curve of the six in the figure represents ^ 

 series of diminishing values of intensities for a single portion 

 of the spectrum, the centre of which has the wave-length 

 indicated on the curve. Each curve also is composed of two 

 straight lines. The change of direction appears to be very 

 abrupt, though probably the sharpness would give place to a 

 somewhat more gradual change if a series of observations 

 were to be made for slight alterations in brightness. 



On comparing the curves it will be noticed that the upper 

 portions of all fall into two groups. Those in the red' 

 orange, and yellow, for the wave-lengths X*725/Lt, \'665 (jl, 

 and A, *590 yit, approach parallelism, the last two being almost 

 exactly so. The remaining curves for green, blue, and violet,.. 



