"The three known papers were those impregnated with the nitrate, chloride, and the iodide of silver--the two former used by Wedgwood and Young, and the latter by Davy. It is true that Talbot says of the iodide of silver that it is quite insensitive to light, and so it is as he makes it; but when he reduces it to the condition described by Davy--viz., affected by the presence of a little free nitrate of silver--then he must acknowledge, with Davy, that 'it is far more sensitive to the action of light than either the nitrate or the muriate, and is evidently a distinct compound.' In this state, also, the infusion of galls or gallic acid is, as we all know, most decided and instantaneous, and so I found it to be in my early experiments. Of course I tried the effects of my accelerator on many salts of silver, but especially upon the iodide, in consequence of my knowledge of Davy's papers on iodine in the 'Philosophical Transactions.' These I had previously studied, in conjunction with my chemical friend, Mr. Hodgson, then of Apothecaries' Hall. I did not, however, use iodised paper, which is well described by Talbot in the _Philosophical Magazine_ for March, 1838, as a _substitute_ for other sensitive papers, but only as one among many experiments alluded to in my letter to Mr. Brayley. "My pictures were exhibited at the Royal Society, and also at Lord Northampton's, at his lordship's request, in April, 1839, when Mr. Talbot also exhibited his. In my letter to Mr. Brayley, I did not describe iodised pictures, and, therefore, it was held that exhibition in the absence of description left the process legally unknown. Mr. Talbot consequently felt justified in taking out a patent for uniting my _known_ accelerator with Davy's _known_ sensitive silver compound, adopting my method (already communicated to him) with reference to Wedgwood's papers, and adding specific improvements in manipulation. Whatever varied opinion may consequently be formed as to the defence of the patent in court, there can be but one as to the skill of the patentee.