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most easily observed. The experiment is an easy one to set up and to repeat. This property of “N” rays is analogous to that of the red and infra-red rays discovered by Edmond Becquerel. It is also analogous to the action of heat on phosphorescence. Nevertheless, I have not noticed as yet an increased rate of exhaustion of the phosphorescent capacity under the action of “N” rays (see p. 74).
The kinship of “N” rays with known radiations of large wave-length seems a certain fact. As, on the other hand, the property possessed by these rays of traversing metals differentiates them from all known radiations, it is very probable that they are comprised in the five octaves of the series of radiations, hitherto unexplored, between the Rubens rays and electro-magnetic oscillations of very small wave-length. This is what I propose to verify (note 8).
On the Existence of Solar Radiations capable
of traversing Metals, Wood, etc. (June 15,
I have recently proved that the majority of artificial sources of light and heat emit radiations which are able to traverse metals and a great number of bodies, opaque in regard to the spectral radiations hitherto known (see p. 18). It was desirable to ascertain whether radiations analogous to the former—which, for brevity, I call “N” rays—are also emitted by the sun.
As I have shown, “N” rays act on phosphorescent substances by heightening or stimulating the pre-existing phosphorescence, an action similar to that of red and infra-red rays discovered by Edmond Becquerel (see p. 74). I utilized this phenomenon to find out whether the sun sends us “N” rays.
A completely enclosed dark room has one window exposed to the sun. This is shut by interior, opaque panels of oak, 15 mms. thick. Behind one of these panels, at any distanceI metre, for instance-a thin glass tube is placed, containing a phosphorescent substance, say calcium sulphide, which has been previously exposed for a short time to solar rays. If, now, on the path of the solar rays, which are supposed to reach the tube through the wood, a sheet of lead, or the hand simply, is interposed, even at a great distance from the tube, the phosphorescent glow is seen to diminish; when the obstacle is removed, the glow reappears. The extreme simplicity of this experiment will incite many persons, I hope, to repeat it. The only precaution one need take is to operate with a feeble preliminary phosphorescence (note 9). It is advantageous to arrange permanently a sheet of black paper, so that the interposition of the screen does not change the background on which the tube stands out. The variations in glow are especially easy to catch near the contours of the luminous patch formed by the phosphorescent body on the dark background; when the “N” rays are intercepted, these contours lose their sharpness, regaining the same when the screen is removed. However, these variations in glow do not appear to be instantaneous. Interposing
between the shutter and the tube several sheets of aluminium, cardboard, or an oak board 3 cms. thick, does not hinder the phenomenon ; any possibility of an action of radiated heat, as such, is consequently excluded. A thin film of water completely arrests the rays ; light clouds passing over the sun considerably diminish their action.
The “N” rays emitted by the sun can be concentrated by a quartz lens; by means of the phosphorescent substance, the existence of several foci is ascertained. I have not yet determined their positions with sufficient precision to speak of them here. The “N” rays of sunlight undergo regular reflection by a polished plate of glass, and are diffused by ground glass.
The “N” rays issuing from the sun increase the glow of a small spark and a small flame in the same manner as those emitted by a Crookes' tube, by a flame, or by an incandescent body. These phenomena are easy to observe, especially if use is made of an interposed sheet of ground glass, as indicated by me in a preceding communication. The use of a
small flame is by far the most convenient and precise of all processes for determining the position of the foci. Operating with the small spark is much harder, because the spark is rarely very regular.
I feel bound to reproduce, textually, here a passage in a letter which M. Gustave le Bon has done me the honour of writing
“M. Gustave le Bon had indicated, as far back as seven years ago, that flames emit, independently of the radio-active emanations since observed by him, radiations of large wave-length, capable of traversing metals, and to which he had given the name of black light; but while assigning these a place intermediate between light and electricity, he had not exactly measured their wave-length, and the method he had employed to reveal their presence was very uncertain.”
The method referred to was the photographic method. Personally, I have not been able to obtain any photographic effect of the rays I have studied (see p. 16).