"N" Rays/On a New Action Produced by "N" Rays, and on Certain Facts Connected with These Radiations
On a New Action produced by "N" rays, and on Several Facts connected with these Radiations (July 20, 1903).
The action of "N" rays on a small flame gave me the idea of trying whether they did not exercise an analogous action on a solid incandescent body. For this purpose a platinum wire, about 0.1 mm. diameter and 15 mms. long, was heated to dull redness by an electric current. A pencil of "N" rays, emitted by an Auer burner, was directed through wood and aluminium screens on this wire, and was concentrated by a quartz lens.
The wire was observed through a plate of ground glass, fixed to the same support as the wire itself, and about 3 cms. in front of it. On displacing the wire, several foci were found, just as with other processes employed to detect "N" rays. The wire being placed at one of these foci, the luminous patch on the ground glass is seen to diminish in brightness when a lead screen, or merely the hand, is interposed; when the obstacle is removed, the light resumes its former brightness. These actions do not appear instantaneous.
I have generalized the former experiments by employing, instead of a wire heated by an electric current, a sheet of platinum 0.1 mm. thick, inclined at 45° on the horizontal plane, partially heated to a dark red by a small gas flame placed underneath. A horizontal pencil of "N" rays, concentrated by a lens, was made to impinge on the under face of the sheet, so as to produce a focus at the heated spot; on the upper face the incandescent patch was observed without interposing ground glass. The variations in brightness are exactly analogous to those of the wire. When observing, through ground glass, the intensity of illumination of the bottom face of the sheet, due to the rays and the flame together, quite similar variations are found. Further, the same results are obtained if, instead of making the rays fall on the lower face, or the side on which the flame acts directly, they are directed upon the upper face.
The different effects produced by "N" rays, viz. their action on a spark or flame, and on phosphorescent or incandescent bodies, would lead to the supposition that they might also have a heating effect on the bodies subjected to their action. To test the matter experimentally, I installed a thermopile of Rubens' connected to an enclosed galvanometer. The action of "N" rays on this apparatus was absolutely nil, even in the most favorable conditions, though a candle placed 12 metres away from the thermopile gave a deflection of about 0.5 mm. on the scale. I conducted the experiment not only with "N" rays proceeding from an Auer burner, but also with those from the sun on the 3rd of July, 1904, at midday. The rays were very intense, for when I placed in front of the thermopile a tube containing calcium sulphide, which had been feebly excited by exposure to the sun, its glow was greatly increased, but was diminished by the interposition of a lead screen or the hand. M. H. Rubens made the same observation, as he was kind enough to write me, his apparatus being much more sensitive even than mine. I nevertheless thought it useful to determine directly whether the incandescent platinum wire was not heated by the action of "N" rays. To this end, I had recourse to the study of its electric resistance. The current flowing through the wire is produced by five accumulators; with the aid of high-resistance rheostats, the intensity is adjusted to make the platinum wire a dull red. The wire is stretched between two massive brass pliers, A and B, which are connected to the terminals of a capillary electrometer; on one of the connecting wires an adjustable electromotive force is inserted, obtained by shunting a portion of the circuit of an auxiliary battery. This electromotive force is regulated so that the electrometer is at zero. Every variation in resistance of the platinum wire produces a deviation of the electrometer. Now, with "N" rays playing on the wire, no deviation of the meniscus was observed. The interposition of a lead or wet-paper screen remained without effect on the electrometer, though the wire underwent the usual variations in brightness. This certainly proves that "N" rays do not raise its temperature. I, moreover, assured myself that the method was sufficiently sensitive by the following experiments; by means of a wire rheostat, an assistant varied the resistance of a circuit containing the platinum wire and the accumulators, and consequently the strength of the current, but not sufficiently for the observer to perceive a variation in the glow of the wire. In spite of this, the electrometer was deflected three divisions of the micrometer in the eye-piece. The following is another verification: raising the temperature of the wire one degree would alter its resistance in the ratio of about 1.004 to one; the difference of potential between A and B would alter in about the same ratio, since, the resistance external to the wire being very great, the current strength does not change. In my experiments this variation would deflect the electrometer by fifteen divisions. As absolutely no deviation occurred, and as, moreover, a quarter of a division could have been easily observed, the rise in temperature is certainly very inferior to of a degree, and, consequently, quite insufficient to produce the observed increase in glow. It is thus super-abundantly established that the increase in glow produced by the rays is not due to a rise in temperature.
In the experiments with a plate of platinum, mentioned above, the increase in glow was apparent on the two faces of the sheet. Given that there is no rise in temperature, this seems paradoxical; for since "N" rays do not go through platinum, it seemed as if the action should only appear on the side exposed to these rays. To reconcile these results, it was necessary to suppose that "N" rays, which do not traverse cold platinum, traverse it when incandescent. I then reverted to the apparatus which was destined to show the action of "N" rays on a small flame, and behind the quartz lens I arranged a platinum sheet larger than the lens. The interposition of a lead screen between the platinum and the source produced no effect on the small flame, which verifies the opacity of platinum. The plate being then heated to redness, interposing the screen was seen to diminish the glow of the small flame. "N" rays issuing from an Auer burner traverse therefore incandescent platinum.