and on the Elementary Colors of the Solar Spectrum. 11 
cond, I perceived that the luminous zones belonging to the ele- 
mentary spectrum were much more sharp, although less intense, 
much narrower, and traversed by obscure zones, much deeper, 
larger, and with contours more striking than those of the spec- 
trum which came from the unpainted part of the prism. It was 
easy thus to convince myself, by the comparative inspection of 
the three images, that the differences of tint between the second 
and third spectrum corresponded to the colors which Sir D. Brews- 
ter imagines to have the same refrangibility as the tints absorbed. 
| his spectrum, for instance, the normal orange color is replaced 
by an obscure zone invaded on one side by the red, and on the 
other by the yellow, from which he infers the presence of these 
two colors in the orange. Now these invasions of the yellow 
red do not exist in my elementary spectrum, in which all the 
Space corresponding to the orange is occupied by a dark zone ; 
the red and the yellow which limit this zone, in the spectrum pro- 
duced by all the middle part of the prism covered by the blue glass, 
are therefore independent of this spectrum, and belong to spectra 
of elementary layers superior and inferior to the intermediate line. 
his last conclusion is nevertheless not exempt from objec- 
tions. For in a dark room the observer must necessarily have 
his pupil much dilated, and his sight be more or less confused ; 
consequently, on locking at one time through the uncovered 
prism, and at another through a limited space of the prism nar- 
rower than the pupil of the eve, it may happen that the greater 
extent of the tints transmitted by the blue glass in the first ob- 
Servation may arise from an indistinct vision, and not from a real 
overlapping of the colors from the superior and inferior parts of 
the prism. This conjecture seems the more plausible since all 
the rays refracted by the prismatic elements, are not perceived by 
e observer, but only those that pass through the aperture of 
il. 
color and darkness of the 
the yellow. 
