272 



NICHOLS— EFFECTS OF TEMPERATURE 



[April 22, 



To cool the phosphorescent compound the lower end of the 

 bronze tube was submerged in a cylindrical Dewar flask containing 

 liquid air and by the vertical adjustment of this tube any tempera- 

 ture from that of the room to about — 185° could be reached and 



t 



N 



% 



J 



Fig. 3 Device for observing the cooled substance. 



maintained. The temperatures were measured by noting the elec- 

 trical resistance of a previously calibrated coil of fine copper wire C 

 (Fig. 2) imbedded in the copper cylinder and immediately sur- 

 rounding and in contact with the capsule. A shutter, the opening 



Fig. 4. The photometer. 



and closing of which was automatically recorded by a chronograph, 

 was used in making exposures to excitation. 



For the determination of the curves of decay a specially de- 

 signed photometer was used. This consisted of a slight tube 0, 

 Fig. 4, mounted horizontally in front of and coaxially with the 



