90 Mr. Claudet on different Properties of Solar Radiation 



Soon after the publication of M. Ed. Becquerel's memoir, 

 M. Gaiidin made some analogous researches on the Daguer- 

 reotype plate ; and he succeeded in developing an image as 

 perfect as that produced by mercury, by submitting the plate, 

 when taken from the camera obscura, to the action of light 

 alone under a yellow glass, and without any subsequent ex- 

 posure to mercury. 



This curious discovery gave some hope that, from the sup- 

 posed continuing action of the red and yellow glasses, by 

 submitting the plate alternately, or simultaneously, to the 

 action of the mercury and of these glasses, an accelerated de- 

 velopment of the image would result ; but all the researches 

 made to arrive at this point have been fruitless ; and, until the 

 present time, the labours of Messrs. Becquerel and Gaudin 

 have received no satisfactory explanation or useful application. 



My own experiments, which are the object of this memoir, 

 seem to prove that M. Ed. Becquerel was mistaken as regards 

 the Daguerreotype plate, in so far as he attributed to the red, 

 orange, and yellow glasses a continuing action of the effect of 

 the photogenic rays. 



In the Daguerreotype, when we speak of the photogenic 

 effect, we cannot understand any other than that which gives 

 to the surface an affinity for mercurial vapour. 



In the case of photogenic papers, it is true that the red, 

 orange, and yellow rays render the parts previously affected 

 bv the photogenic rays black or of a darker colour. It is the 

 same with the Daguerreotype plate, which after it has been 

 feebly impressed, darkens rapidly to a violet colour under the 

 radiation of a red or yellow giass. This is the only continuing 

 effect I have observed, and this effect is not continuing in a 

 Daguerreotype sense, it has no relation to the property of 

 attracting the mercurial vapour; on the contrary, it will be 

 seen from the experiments which I am about to describe, that 

 the radiations of red, orange and yellow glasses entirely destroy 

 this property. There exists then a certain analogy between 

 the action of the red, orange and yellow glasses upon the pho- 

 toi^enic papers and the Daguerreotype plate; and this conti- 

 nuing action is probably due to the distinct photogenic action 

 possessed by these rays, as I am able to prove by facts of a 

 very positive nature. 



These two photogenic actions result from two different 

 principles, nevertheless producing similar effects, as to the 

 colour obtained, on the iodide, bromide or chloride of silver, 

 whether it be fbunil isolated, as is the case on the photogenic 

 paper, or it be found in the presence of metallic silver, as 

 happens upon the Daguerreotype plate ; but they produce 



