A Manual Of Photography

THE CALOTYPE. 23 east without essentially altering, the causes which produce their c iarm; and then, tor the purposes which I have mentioned, papers very susceptible of impression would still have the advan- ages of being less troublesome in removal from place to place, as also of more easy preservation. The utility of sensitive papers for copying texts was a natural consequence of the clearness of the copies of engravings which Mr. lalbot had already obtained by application, and which were presented to the Academy. He has included others among those just sent: there are also added specimens of this especial appli- cation consisting of copies of a Hebrew psalm, of a Persian Suzette, and of an old Latin chart of the year 1279. Our re neu of the Académie des Belles Lettres, to whom I exhibited hese impressions, were pleased to remark the fidelity of the c ^racters, and their clearness, by whieli they are rendered as egible as the original text. Doubtless an old manuscript may be copied more quickly and more accurately by this means than by hand, oven when the language in whieli it is written is understood. However, we must stop here. These copies are obtained by application: we must be enabled to obtain them by immediate radiation in the camera obscura. It is the only means of extending the process to papyrus and other opaque manuscripts, or which are not sufficiently transparent for radia- tion to traverse them. Moreover, the application of leaves is very difficult when they are bound up in a volume, and cannot be detached from one another. But tliis important extension will require much physical per- tectmg, towards which experimenters should direct their efforts. The first thing will be to augment the sensibility of the paper as much as possible, in order that the capillary communication of its various parts may not have sufficient time to deteriorate the effects of the local and immediate action of the radiation. I should be led to believe that it is principally to this kind of communication should be attributed the fact remarked by Mr. lalbot, that, in experiments by application, it is more difficult to copy clearly a tissue of black lace spread on a white ground, than white lace on a black ground ; two cases of whieli he here gives examples. But another more hidden and more general difficulty seems to me to proceed from the unequal faculty of various substances for reflecting the radiations which strike them, and perhaps from their aptitude for making them undergo physical modifications. For example, you wish to copy by radiation in the camera obscura a picture painted on canvas wood, or porcelain : the different colouring substances employed by the painter are placed and distributed in such a manner that