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on record a number of insulated facts and observations respecting 

 the relations both of white light, and of the differently refrangible 

 rays, to various chemical agents which have offered themselves to his 

 notice in the course of his photographic experiments, suggested by 

 the announcement of M. Daguerre's discovery. After recapitulating 

 the heads of his paper on this subject, w^hich was read to the Society 

 on the 14th of Mai'ch, 1839, he remarks, that one of the most im- 

 portant branches of the inquiry, in point of practical utihty, is into 

 the best means of obtaining the exact reproduction of iu definitely 

 multiplied facsimiles of an original photograph, by which alone the 

 publication of originals may be accomplished ; and for which purpose 

 the use of paper, or other similar materials, appears to be essentially 

 requisite. In order to avoid circumlocution, the author employs the 

 terms positive and negative to express, respectively, pictures in which 

 the lights and shades are the same as in nature, or as in the original 

 model, and in which they are the opposite ; that is, light represent- 

 ing shade ; and shade, light. The terms direct and reverse are also 

 used to express pictures in which objects appear, as regards right 

 and left, the same as in the original, and the contrary. In respect 

 to photographic publication, the employment of a camera picture 

 avoids the difficulty of a double transfer, which has been found to 

 be a great obstacle to success in the photographic copying of en- 

 gravings or drawings. 



The principal objects of inquiry to which the author has directed 

 his attention in the present paper, are the following. First, the means 

 of fixing photographs ; the comparative merits of different chemical 

 agents for effecting which, such as hyposulphite of soda, hydiiodite 

 of potash, ferrocyanate of potash, &c., he discusses at some length ; 

 and he notices some remarkable properties, in this respect, of a pe- 

 culiar agent which he has discovered. 



2. The means of taking photographic copies and transfers. The 

 author la3'S great stress on the necessity, for this purpose, of pre- 

 serving, during the operation, the closest contact of the photogra- 

 phic paper used with the original to be copied. 



3. The preparation of photographic paper. Various experiments 

 are detailed, made with the view of discovering modes of increasing 

 the sensitiveness of the paper to the action of light ; and particularly 

 of those combinations of chemical substances which, applied either 

 in succession or in combination, prepare it for that action. The ope- 

 ration of the oxide of lead in its saline combinations as a mordent 

 is studied ; and the influence which the particular kind of paper 

 used has on the result, is also examined, and various practical rules 

 are deduced from these experiments. The author describes a method 

 of precipitating on glass a coating possessing photographic proper- 

 ties, and thereby of accomplishing a new and curious extension of the 

 art of photography. He observes, that this method of coating glass 

 with films of precipitated argentine, or other compounds, affords 

 the only effectual means of studying their habitudes on exposure to 

 light, and of estimating their degree of sensibility, and other parti- 

 culars of their deportment under the influence of reagents. After 



