H. Garbanati, in an article on this subject in the American Journal of Photography, tells us the following: — " I was recently handed two small pieces of glass, in the center of each was a dark object, about a quarter of an inch square. In the center of the square of one of these, by dint of close and painful examination, I discovered a speck about one-sixteenth of an inch diameter, which bore somewhat the resemblance to a portrait of a head. In the other was also a speck about one-eighth of an inch, and some other very minute specks in the one speck, but which I could not recognize as any particular objects. By holding the first piece of glass up to the light, and looking through a powerful magnifier, I discovered a perfect portrait of about a sixth size, and in the other a group of five equally perfect, of about half size. To what use might not this mode of photographing be put ? In war the most elaborate instructions might be carried in a button or head of a pencil-case ; and the general or secretary of war needs but a magnifying glass to save the use of spies and men from hanging. The whole archives of a nation might be packed away in a snuffbox. Had the art been known in the time of Omar, the destruction of the Alexandrian library would not have been a final loss." i