174. J. W. Draper—Phosphorograph of a Solar Spectrum. 
Nothing like sharpness of definition could be obtained except 
in very brief exposures before the effect had had time to 
spread. 
ay, EXaMINATION or PuospnorEscent TABLETS BY GELATINE 
PHOTOGRAPHY. 
The examination of a phosphorescent surface can be made 
now in a much more satisfactory manner than formerly. The 
light we have to deal with, being variable, declines from the 
moment of excitation to the moment of observation. And, 
though the phosphori now prepared are much more sensitive 
looked upon as ephemeral. To examine them properly, the 
eye must have been a long time in darkness to acquire full 
sensitiveness. 
was recommended by Dufay to place a bandage over one 
eye that its sensitiveness might not be disturbed, whilst the 
other being left naked could be used in making the necessary 
preparations. But this on trial will be found, though occasion- 
ally useful, on the whole an uncomfortable and unsatisfactory 
hod. 
The exceedingly sensitive gelatine plates now obtainable 
remove these difficulties. The light emitted by blue phosphor!, 
such as luminous paint, consists largely of rays between and 
