( 87 ) 
returning to their original position of equilibrium, cause the emission 
of phosphorescent light. The motion of the electrons causing phos¬ 
phorescence, and therefore, the position of the bands in the spectrum 
will, of course, undergo different modifications for the various salts 
by the influence (of the electric field) of the other atoms, which with 
the atom of uranium form a complete molecule. 
EXPLANATION OF THE FIGURES. 
Fig. 1. Potassium uranyl sulphate a) at 288° K, b) at 80° K, c) at 20° K. 
First spectrum, Rowland grating. 
The spectra a) and 6) photographed beside each other on the same 
plate allow a direct comparison of the positions of the bands at 
ordinary temperature and at that of liquid nitrogen. 
Fig. 2. a) Autunite (Calcium uranyl phosphate). 
b) Potassium uranyl chloride. 
c) TJranyl nitrate. 
d) Potassium uranyl sulphate. 
Temperature 80° K. First spectrum, Rowland, grating. 
Fig. 8. a) and c ) Potassium uranyl chloride, 
b) and f) Uranyl nitrate, 
g) Potassium uranyl sulphate, 
d) Autunite (calcium uranyl phosphate). 
Temperature 14° K. Second spectrum, Rowland grating. These photos 
give the details of the groups at the temperature of solid hydrogen. 
Fig. 4 and 5. Potassium uranyl sulphate. 
a) at 14° K., b) at 20°K., c ) at 80°, K. 
Second spectrum, Rowland grating. Details of the groups at these 
three temperatures. 
Fig. 6. Adjacent spectra of a) potassium uranyl sulphate at 20° K. and b) 
the iron arc. 
Second spectrum, Rowland grating. Example of the measurement of 
wave-length; short exposure so as to make an accurate measurement 
possible. 
Fig. 7. Sodium uranyl acetate at 80° K. 
First spectrum, Rowland grating. 
Measurement of wave-lengths, and details of the groups. 
Fig. 8. a) Iron arc , b) Sodium uranyl sulphate , c) Ammonium uranyl 
sulphate. 
Temperature 80° K. 
First spectrum, Rowland grating. 
Measurement of wave lengths, and details of the groups. 
Fig. 9. Uranyl sulphate at 80° K. 
Fig. 10. a) Iron arc, b) Uranyl sulphate. 
Temperature 80° K. 
First spectrum, Rowland grating. 
Channeled spectrum in the yellow and orange. 
