POPULAR SCIENCE MONTHLY.
them as a material radiation, and which, as it appears to me, might be thus enunciated. In the neighborhood of the cathode, the electric field is sufficiently intense to break into pieces (into ions) certain of the molecules of the residual gas. The negative ions move toward the region where the potential is increasing, acquire a considerable speed, and form the cathode rays; their electric charge, and consequently their mass (at the rate of one valence-gramme for a hundred thousand coulombs), is easily measurable. The positive ions move in the opposite direction; they form a diffused brush, sensitive to the magnet, and not a radiation in the correct sense of the word."
Nikola Tesla, in a recent Electrical Review, describes the following experiment, which seems to support the view that these rays are material radiations: When an exhausted bulb is attached to the terminal of a disruptive coil, small streamers are observed which often break through the side of the bulb, producing a fine hole. "Now, the extraordinary thing is that, in spite of the connection to the outer atmosphere, the air can not rush into the bulb as long as the hole is very small. The glass at the place where the rupture is may grow very hot—to such a degree as to soften; but it will not collapse, but rather bulge out, showing that a pressure from the inside greater than that of the atmosphere exists. On frequent occasions the hole becomes so large as to be perfectly distinguishable to the eye. As the matter is expelled from the bulb the rarefaction increases and the streamer becomes less and less intense, whereupon the glass closes again, hermetically sealing the opening." He reports producing strong pictures at a distance of forty feet by the use of a bulb with a single terminal, which permits the use of practically any desired potential.
An account of some important experiments by L. Benoist and D. Hurmuzeson appears in the Comptes Bendus. They caused the rays of a Crookes tube, incited by a powerful coil, to act upon the gold leaves of a Hurmuzeson electroscope at the distance of about twenty centimetres from the tube, and alternately charged with positive and negative electricity. The insulation obtained by a disk of dielectrine which closes the tube admits of the perfect preservation of its charge for several months. The X rays immediately and completely discharge the electroscope, more rapidly if the charge is negative than if it is positive. "We have thus," they say, "a new way of investigation applicable to the study of these rays, and enabling us to gain important information as to their real nature. The plate to be studied being put in its place, the electroscope charged to about a divergence of forty degrees, the keeping tube replaced, and the Crookes tube set in activity, we have observed: