260 
MR. CLAUDET ON DIFFERENT PROPERTIES OF SOLAR RADIATION 
under these lines had been protected from the destructive action, received the mercury, 
producing a negative image ; while the same radiation of the yellow glass had ope- 
rated photogenically upon the other half, developing a positive image by the fixation 
of mercury upon the parts corresponding to the lights of the engraving. 
Having exposed a plate with an engraving under the red glass for sixty minutes, I 
replaced the red by a yellow glass, without the engraving ; after exposing the half 
of this plate for five minutes under this yellow glass, the other half being kept in the 
dark, the mercury produced a negative image on the half exposed to yellow light, 
while the other gave no trace of either positive or negative action. This result can 
only be explained in the following manner : — 
First. That sixty seconds had not sufficed for the apparent action of the red upon 
the half not exposed to the following radiation of the yellow glass. 
Secondly. That nevertheless there had been the commencement of an action upon 
which the yellow glass had to exercise its destructive action. 
Thirdly. That while the yellow glass was occupied in destroying the photogenic 
action of the red glass, restoring the surface to its primitive state, it was exercising 
a photogenic action upon the parts protected by the engraving from the red rays, 
and in five minutes this photogenic action of the yellow glass had produced a nega- 
tive image by operating upon the shadows of Xhe drawing. 
It results from the experiments I have described, that the solar radiation, when 
modified by coloured media, is in the Daguerreotype process endowed with several 
different photogenic actions, corresponding with various rays of the spectrum. 
The various photogenic actions of the modified solar radiation have distinct cha- 
racters ; each of these modifications is endowed with a photogenic power peculiar to 
itself, and which gives an affinity for mercurial vapour to the Daguerreotype plate. 
These various actions are so different, that we cannot mix them artificially to assist 
each other, as they are antagonistic. The effect commenced by the blue rays is de- 
stroyed by the red and yellow ; that which was produced by the red is destroyed by 
the yellow ; the effect of the yellow rays is destroyed by the red ; and the effect of 
the two latter is destroyed by the blue ; each radiation destroys the effect of the 
others. Thus it appears that each radiation changes the state of the surface, and 
each change produces the sensitiveness to mercurial vapour when it does not exist, 
and destroys this sensitiveness when it does exist. 
The alternate change of the state of the plate by these various radiations seems to 
prove that the chemical compound remains always the same under these different 
influences ; that there is no separation or disengagement of the constituent elements. 
If the blue radiation or white light liberates iodine or bromine, these elements would 
evaporate or combine with the silver surface immediately beneath. If we take the 
first idea, how comes it that the red radiation re-establishes the compound in its pri- 
mitive proportions ; and, in the second case, how does it happen that these rays are 
capable of decomposing the surface beneath, liberating the iodine or bromine, and 
