128 



STUDIES IN LUMINESCENCE. 



of 20 units. The intensities of the acetylene flame were 32, 20, 12, and 6 

 for curves 1, 2, 3, and 4 respectively. Curve 6 is assumed to represent the 

 energy distribution in curve 4. Curve 5, which shows the distribution of 

 energy in the fluorescence light, is similar to the corresponding curve 5 in 

 Fig. 133. This shows that the curve is not materially influenced by two 

 factors, length of exposure and width of slit in the spectroscope. 



The Sidot blende was excited by three blue lines of the mercury-are 

 spectrum. While these lines are in a different region of the spectrum from 

 that occupied by the fluorescence band, yet there was considerable halation 

 shown on the plates about the three lines and it was thought that this might 

 extend far enough to change the shape of the curves in the region of smaller 

 wave-lengths. 



To test this matter a slab of magnesium carbonate was substituted for the 

 Sidot blende and was illuminated in the same manner by the blue and 

 violet lines of the mercury arc. 



A plate was exposed to the light reflected from this slab and also, as in 

 the previous experiments, to four different intensities of acetylene light. 

 Curves showing the amount of transmitted light are given in Fig. 136. 



.66 



AZ .4-6 .50 .54 .58 .62 



Fig. 136. 



In this as in the previous figures curves 1 , 2,3, and 4 are for the acetylene 

 light. Curve 5 indicates the transmission of that part of the plate exposed 

 to the light of the mercury arc reflected by the magnesium carbonate. 

 vSince there is no indication of any effect it appears that halation from the 

 mercury lines is inappreciable for wave-lengths longer than 0.46 \x and that 

 no error from this source occurs in the curves marked 5 in Figs. 133 and 135. 



Experiments were also made with very intense negatives in an endeavor 

 to obtain the shape of the energy curves for wave-lengths greater than 0.60 /i, 

 but on account of an apparent tendency to reversal in such negatives it was 

 not found possible by this method to extend observations to these longer 

 waves. 



PHOSPHORESCENCE AT ROOM TEMPERATURE. 



In order to obtain the distribution of energy in the phosphorescence 

 light, it was necessary to add to the apparatus already described a shutter 

 which would close the spectrum camera and excite the powder; then shut 

 off the exciting light and open the camera. The shutter was operated by 

 a constant-speed motor. Levers, springs, and triggers were so arranged 



