action on a small spark. I asked myself if the spark should in this case be considered as an electric phenomenon, or only as producing incandescence like a small gaseous mass. If this latter supposition were correct, the spark could be replaced by a flame. I then produced a quite small flame of gas at the extremity of a metal tube having a very small orifice. This flame was entirely blue. I ascertained that the flame could be used to reveal the presence of "N" rays just like the spark; for when it receives these rays, it becomes whiter and brighter in just the same way. Its variations in glow allowed of four foci being found in a pencil which had passed through a quartz lens; these foci are the same as those detected with the small spark. The small flame behaves therefore, in regard to "N" rays, just like the spark, save that it does not allow of the observation of polarization phenomena.

In order to study more easily the variations in glow, whether of flame or spark, I examine them through a plate of ground glass, about 25 or 30 mms. distant. In this way one obtains,

instead of a very small, brilliant point, a luminous patch of about 2 cms. diameter, of much less luminosity, whose variations can be far better appreciated by the eye.

The action of an incandescent body on a flame, or that of a flame on another flame, is certainly a common phenomenon. If it has remained unnoticed up to the present, it is because the light of the source prevented the observation of the variations in glow of the receiving flame.

Quite recently I observed another effect of the "N" rays. It is true that these rays are unable to excite phosphorescence in bodies which can acquire this property under the action of light, but when such a body-calcium sulphide, for instance-has previously been rendered phosphorescent by exposure to sunlight, if it is then exposed to "N" rays—for instance, to one of the foci produced by a quartz lens-the phosphorescent glow is observed to increase in a very marked fashion; neither the production nor the cessation of this effect appear to be absolutely instantaneous. Of all the actions producing "N" rays, this is the one which is

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, 1903).

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