1 66 STUDIES IN LUMINESCENCE. 



When the tube was newly made up the electrometer remained quiet under 

 all conditions, except for an occasional drift of not more than i division in 5 

 seconds. In the earlier work, after a few heatings, the electrometer began 

 showing a tendency to rise rather quickly to a more or less definite deflection, 

 regardless of conditions of potential or illumination. This peculiar effect 

 varied from run to run and became very great in a case or two when the 

 cement with which the tube was sealed cracked and admitted air. A brown 

 deposit was then left in the tube, apparently the result of a combination of 

 the oxygen of the air with the anthracene. 



A possible explanation of this attainment of a steady deflection even 

 when the outer electrode was earthed is that the product of the decom- 

 position of the anthracene is deposited on the quartz tube separating the 

 silver guard-ring from the inner electrode and forms with these two metals 

 a sort of voltaic cell. This "cell" had a very high temperature coefficient 

 and in some cases the E.M.F. was so great as to throw the spot of light off 

 the scale. 



After several trials it was found possible, by taking great care to prevent 

 the entrance of air, to get almost entirely rid of this effect. The elec- 

 trometer then behaved normally. 



No ordinary conduction was found. If the light had any effect it was 

 too small to be detected. Thinking that the vapor under the action of the 

 light might be almost ionized, an attempt was made to help out the ioniza- 

 tion by exposing the vapor to the action of a small sample of radium 

 bromide. The ionizing rays from this substance did not pass through the 

 glass sufficiently to be of any use. 



Higher potential was obtained by making up a set of small lead sul- 

 phuric acid storage cells in test-tubes. This battery, when put in series 

 with the one already at hand, gave from 360 to 540 volts, depending upon 

 the condition of the small cells. The sensibility was increased by charging 

 the electrometer needle to 120 volts. With the greater sensitiveness and 

 the unsteady potential furnished by the cells, the electrometer wandered 

 more or less in the neighborhood of the zero, but still did not indicate any 

 steady rate of charging such as would have been evident had there been 

 appreciable conductivity of the vapor. 



In the freshly exhausted tube the pressure was so low that the application 

 of 400 volts caused a continuous luminous discharge through the tube, but 

 this soon disappeared as the pressure rose due to the vaporization of the 

 anthracene. 



The number of trials was great enough to leave no doubt as to the be- 

 havior of the vapor under the various conditions mentioned. 



CONCLUSIONS. 



1. The conductivity of anthracene vapor at the temperature and density 

 used in this experiment is too small to measure in the manner described. 



2. The effect of fluorescence, if any exists, is too small to be detected 

 by the very delicate method employed. 



