A current of electricity sent through the former reproduces the writing exactly upon the latter, which has been previously steeped in some chemical composition; the effect apparently depending on the passage of the electricity through the untouched metal, and its absolute interception by the ink, if I may so call it, of the writing, which bites deeply into the leaf.

This process can be repeated almost _ad libitum_; and it is equally easy to take at any time a fresh copy upon _tafroo_, which serves again for the reproduction of any number of _difra_ copies.

The book, for the convenience of this mode of reproduction, consists of a single sheet, generally from four to eight inches in breadth and of any length required.

The writing intended to be thus copied is always minute, and is read for the most part through magnifying spectacles.

A roller is attached to each end of the sheet, and when not in use the latter is wound round that attached to the conclusion.