In the-well equipped Jackson laboratory at Trinity College, Hartford, I found Dr. W.L. Robb, the professor of physics, surrounded by enthusiastic students, who were assisting him in some experiments with the new rays. Dr. Robb is the better qualified for this work from the fact that he pursued his electrical studies at the Würzburg University, in the very laboratory where Professor Röntgen made his great discovery. The picture reproduced herewith, showing a human foot inside the shoe, was taken by Dr. Robb. The Crookes tubes used in this and in most of Dr. Robb's experiments are considerably larger than any I have seen elsewhere, being pear-shaped, about eight inches long, and four inches wide at the widest part. It is, perhaps, to the excellence of this tube that Dr. Robb owes part of his success. At any rate, in the foot picture the bones are outlined through shoe and stocking, while every nail in the sole of the shoe shows plainly, although the rays came from above, striking the top of the foot first, the sole resting upon the plate-holder. In other of Dr. Robb's pictures equally fine results were obtained; notably in one of a fish, reproduced herewith, and showing the bony structure of the body; one of a razor, where the lighter shadow proves that the hollow ground portion is almost as thin as the edge; and one of a man's hand, taken for use in a lawsuit, to prove that the bones of the thumb, which had been crushed and broken in an accident, had been improperly set by the attending physician. [Illustration: THOMAS A. EDISON EXPERIMENTING WITH THE RÖNTGEN RAYS.] Dr. Robb has made a series of novel and important experiments with tubes from which the air has been exhausted in varying degrees, and has concluded from these that it is impossible to produce the Röntgen phenomena unless there is present in the tube an almost perfect vacuum. Through a tube half exhausted, on connecting it with an induction coil, he obtained merely the ordinary series of sparks; in a tube three-quarters exhausted, he obtained a reddish glow from end to end, a torpedo-shaped stream of fire; through a tube exhausted to a fairly high degree--what the electric companies would call "not bad"--he obtained a beautiful steaked effect of bluish striæ in transverse layers. Finally, in a tube exhausted as highly as possible, he obtained a faint fluorescent glow, like that produced in a Crookes tube. This fluorescence of the glass, according to Dr. Robb, invariably accompanies the discharge of Röntgen rays, and it is likely that these rays are produced more abundantly as the fluorescence increases. Just how perfect a vacuum is needed to give the best results remains a matter of conjecture. It is possible, of course, as Tesla believes, that with an absolutely perfect vacuum no results whatever would be obtained.