172 J. W. Draper—Phosphorograph of a Solar Spectrum. 
extending from the boundary of the blue and green to the 
inferior theoretical limit of the prismatic spectrum, 1s a region 
strongly marked in which the action of the daylight has been 
altogether arrested or removed, the daylight and the sunlight 
having apparently counterbalanced and checked each other. 
3. A similar protected region occurs beyond the violet. This, 
however, is very much shorter than the preceding. The sketch 
annexed to Herschel’s paper represents these facts as well as 
they can be represented by an uncolored drawing. 
II. DescrirTION oF THE PHOSPHOROGRAPHIC SPECTRUM. 
In a phosphorograph on luminous paint the same general 
effects appear. If the impression of the spectrum be taken 10 
the absence of extraneous light, there is a shining region oS 
sponding to the blackened region of the photograph. But 1, 
reviously or simultaneously, extraneous light be permitted to 
2 resent, new effects appear. The shining region of the 
phosphorograph has annexed to it, in the direction of the less 
refrangible spaces and extending toward the theoretical limit 
84 t may be separated into its constituent bands, oto 
are very discernible when registered on gelatine as presen y 
descri And since this is not so easily done with the uppe 
the thermopile than those lines. The blackness is then Te 
sumed. It extends to a short distance, and there the phospho- 
rographic impression comes to an end. £ 
This shining rectangle has long been known to students 0 
hosphorescence, but its interesting origin has not until now 
en explained. 
But more, just beyond the region of the violet, the same 
kind of action oceurs,—a dark space, which, however, is of very 
much less extent than that beyond the red. 
The photograph and the phosphorograph thus present athe 
points of similarity. But though there are these striking p0!? 
of resemblance, there are also striking differences. h 
n a spectrum four or five centimeters long, though the pho 
e spectrum must be dispersed much more before they 
can be discerned. 
