Roentgen Ray Lamps and Other Experiments

A vacuum tube, the inner portion of which has fused to it crystals of tungstate of calcium when exhausted to the X-ray stage, gives out scarcely any of the rays; on the other hand, the tubes shine with a splendid white fluorescence. We have here a true fluorescent lamp, possibly commercial, as a very small bulk gave in the photometer 2½ candle power with an extremely small amount of energy. The white light is of a character not unpleasant, but quite the contrary. The spectroscope reveals the reason; the spectrum has strong red rays.

Tubes with aluminum electrodes become coated with transparent aluminum, which, as time goes on, gets so thick as to become visible. The X-ray is greatly diminished, not, I think, so much on account of absorption of the wave after generation, but through lack of elasticity, the concussive action or energy being absorbed by deforming the aluminum.

Silicon carbide is a conductor for high-tension current, a fact previously noted by Tesla. It is a very good conductor. I have substituted pieces of the carbide for aluminum; no air comes therefrom; it does not absorb air; it cannot be melted, nor does it blacken the glass. The voltage can be increased to a point where the glass melts. It may possibly prove the most practical substance for electrodes in high vacua. The only difficulty is the contact between the carbide and platinum wire.

With all glass used for making bulbs the sodium line shows in the spectroscope; there is evidently a decomposition due to the current, electrolytic or otherwise. Combustion tube glass has the least; lime soda glass, that is, the glass used for dry plate photography, has the most. This latter glass is the most transparent to the X-ray, but the continuous decomposition of the glass makes it almost impossible to maintain a vacuum except when connected to the pump, and even then the effect of the current is greater in producing gas than the capacity of the pump to exhaust, but the ray is very powerful.

Experiments were made with over twelve hundred substances in the form of crystals and precipitates. Not one fluoresces through thick cardboard when the sources of energy are the arc light, a six-inch spark in air, a vacuum tube with vacuum so high that a ten-inch spark leaves it dark, and the direct rays of the sun from 11 till 2 p. m.

Another fact supporting the theory that the X-ray is a wave due to concussion is that crystals of calcium tungstate are very sensitive to agitation or slight friction, giving off light. It is also of interest to note that by a properly arranged sensitive flame and phonographic listening tubes, my assistants have made it responsive to the X-ray.