Calotype, 1841, 3 minutes.

Collodion, 1851, 10 seconds.

Collodion (Emulsion), 1864, 15 sec.

Gelatine, 1878, 1 second.

Distance of the object from the plate plays a big part in cathode photography. The successful photographs of the human hand have been those where the palm was facing the cathode, which put the bones nearer the plate by a very little. The greatest interest in the experiments is because of its application to surgery. Glass can be easily detected in the hand and in the foot.

The question of advance rests upon a better transmitter. In this respect it is in the same position that the telephone was in 30 years ago, when, with difficulty, sound could be transmitted only 30 miles.

At this point Professor Trowbridge had several pictures thrown on the screen. The first was of several coins which had been in his pocket-book which had been put in a wooden box that had been surrounded by a pasteboard box. The next picture was of a turkey's wing which showed the bones and a bullet which had been shot into it. The third picture was again of a turkey's wing with three shots in it, and a ring taken by a to and fro current which is the professor's way of finding out the distance of the object from the surface. The last picture was one of a living human hand taken in Hamburg, Germany. It is the best picture ever taken and was exposed an hour.

"The stories of revealing the whole skeleton," Professor Trowbridge concluded, "are very much overdrawn. There is possibly a better arrangement in Germany, but here photographs can not be taken as yet through a greater thickness than the wrist. At present our experiments are limited to the hand and to children perhaps. My work has been devoted chiefly to shortening the time of exposure necessary and to getting parallel rays. I have succeeded so far in penetrating only about an inch of human flesh, but even this much, when applied to the surgery on the hand will alleviate much suffering."

Professor Trowbridge may shortly give another lecture on the same subject. It will be more scientific in its nature.