A Manual Of Photography

34 HISTORY OF PHOTOGRAPHY. adjustment of the proportions, and in the mode of operation, lies the difficulty of these investigations, since it is possible, by adopting other proportions and manipulations not very greatly differing from the above, and which a careless reader might consider to be the same, not only to fail in obtaining the highly exalted sensibility which is desirable in this process, but actually to obtain scarcely any photographic result at all." Mr. Talbot proposed the name of Amphitype, or doubtful image, for these pictures. This name had, however, been adopted previously, at Mr. Talbot’s recommendation, by Sir John Herschel, and in the Collodion processes, to be by and by de- scribed, we have similar phenomena, to which the name applies with equal force. It is not improbable but the high degree of sensibility which is certainly obtained in this process, is rather due to the forma- tion of an iodide of ethyle in tire mixture, than to the com- bination, as Mr. Talbot supposes, of the proto-iodide and the proto-sulphate of iron. My own researches convince me that we should seek for the highest degrees of sensibility amidst the numerous combinations of the ethyle and methyle compounds with the metallic oxides.