3G 
nEPORT—1847. 
Having directed a camera obacura upon the sun, when its disc appearedqnittrd, 
he obtained aAer ten seconds a black image of the sun. The red sua had prohitk 
no photogenic effect, although the surrounding spaces had been Baffidently aSeebi 
by the photogenic rays proceeding from the zenith to attract the white rapoonn 
tnercar)'. This prov^ that the roil rays bad no photogenic power. 
In another experiment he left tlie plate in the camera for twenty minata, ^ 
■an had passed over a long space of the plate, and there resulted a lone mustofi 
tun quite black throughout, so that not only the red sun had produced no ph^ 
nic action, but the red rays had destroyed the effect produced pre\‘iot)8iotl)es*u 
passage. . ■ ji, 
I le then operated in a different manner, not content with the slow moto « * 
sun ; he moved the camera ubscura from right to left and vice wad, loweragfiso 
time by means of a screw. 
1 n this manner the aun had passed rapidly over five or six zones of the plsJf ^ 
pa»aa^ was marked by long black bands, whilst the interveniog spaces 
showing again that it was sufficient in order to destroy the action of the 
rays to let red rays pass rapidly over the spaces prwbusly affected bjrtnepiJ®' 
genic rays. 
lie operated afterwards with coloured glasses. After having taken uponai^' 
reotype plate the impression of a black lace by white light, he covere^*^ 
the plate and exposed the other half to the radiation of a red glass. 
developed an image of the luce on the part which had bc?on ac^ on ont^^ 
white light, and the other which had afterwards received the action of the 
remained black. The rod glass had destiwed the photogenic effect, M w*! 
place with the red light of the sun. . 
He made the same experiments with orange and yellow glasses, andobteiflW 
logous results, but in different periods of time. . y- 
'Fhese oxperiraent.s proved that the red, orange and yellow rays destroy 
of photogenic light, whether these ravs be produced by the dispersion of ^ l^’ 
or by the action of coloured media; but M. Ciaudet believes that lie was tte b^. 
observe, that after the destruction of the photogenic effect the plate is 
stort^ to its former sensitivenoss to white light. , . 
After exposing a plate to the daylight, and then submitting it to tlie » 
artion of red, orange or yellow rays, it will be found again sensiUw totw- 
white light. 
It appears from M. Claudel’s observations that a plate may be expos ri tP 
wUons alternately for any number of times without altering the fioa' 
he surface, which will be invariably sensitive to the vapours of 
been lastly exposed to the action of white light, and that it will bedepnw* 
Bcnsitivcness if it has been lastly exposed to the restoring action of the «"■ 
or yellow rays. * - 
It results from the restoring action of the red, orange and yellow rays. 
gueiTTO^-pe plates may be prepared in open light, and that to give ^ 
new It 18 only necessary to iilace them for some minntes under red P**’^ 
putting them in the camera obscura. This will be advantageous to 
to places where it is difficult to find dark rooms to 
^ides the destructive action of the red. orange and vellow glaWli^ ^ 
pliotogenic action of their*own. that is to^' 
f of causing the fixation of mocuri**^ 
radiations arc endowed with two contrary action?, 
of .•ffbet of the photogenic light, and the other analogous to the effect <rt ^ ^ 
‘Effect of the red rays is 5000 times longer than tb* ^ 
wi,!.;*' '® 50 times, and the yellow only 10 times. H 
connoi Kn off exposed to the destructive action of any ^ 
effect. photogcuically by the radiation which has destmjw 
W ,lVr.t the other radiations. . 
another. destructive action of any radiation cannot oe r® 
