"N" Rays/On the Storing of "N" Rays by Certain Bodies

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On the Storing-up of "N" rays by Certain Bodies (November 9, 1903).

In the course of my researches on "N" rays, I had occasion to note a very remarkable fact. The "N" rays were produced by an Auer burner enclosed in a lantern, and after passing through one of the sides of the lantern, formed by a sheet of aluminium, were concentrated by a quartz lens upon phosphorescent calcium sulphide.[1] The Auer burner having been extinguished and removed the phosphorescent glow, to my great surprise, remained almost as strong as ever, but was darkened by the interposition of lead, or wet paper, or the hand, between the lantern and the sulphide. Nothing was altered by the suppression of the Auer burner, except that the observed actions grew progressively weaker. At the end of twenty minutes they still existed, but were scarcely noticeable.

Studying closely the circumstances of the phenomenon, I was not long in recognizing that the quartz lens had itself become a source of "N" rays; for when this was removed, all action on the sulphide ceased, whereas if it was brought nearer the sulphide, even laterally, the latter would become more luminous. I then took a quartz plate 15 mms. thick, whose surface formed a square of 5-cm. sides, and exposed this to the "N" rays emitted by an Auer burner through two sheets of aluminium and some black paper. It became as active as the lens; when brought nearer the sulphide, it seemed, according to Bichat's expression, as if a veil darkening it was being removed. A still more marked effect was obtained by interposing the quartz plate between the source and the sulphide, quite close to the latter.

In these experiments, the secondary emission by the quartz is added to the "N" rays directly emanating from the source. This secondary emission has, indeed, its origin in the whole mass of the quartz, and not at the surface only, for if several plates of quartz be successively placed on top of each other, the effect is seen to increase with each added plate. Iceland spar, fluor spar, barite, glass, etc., behave like quartz. The filament of a Nernst lamp remains active for several hours after the lamp is extinguished.

A piece of gold, laterally brought near to the sulphide while it is being subjected to "N" rays, increases its glow (note 10); lead, platinum, silver, zinc, etc., produce the same effects. These actions persist after the extinction of "N" rays, as in the case of quartz. Nevertheless, the property of secondary ray emission only permeates slowly through a metallic mass. Thus, if one of the faces of a sheet of lead 2 mms. thick has been exposed to "N" rays for several minutes, this face alone shows activity; an exposure of several hours is necessary for the activity to reach the opposite face.

Aluminium, wood, dry or wet paper, and paraffin do not enjoy the property of storing "N" rays. Calcium sulphide, on the other hand, does possess this property. When I put a few grams of sulphide in an envelope, and then exposed the envelope to "N" rays, I found that its proximity was sufficient to reinforce the phosphorescence of a small mass of previously excited sulphide. This property explains a constant peculiarity that I have previously set forth, viz. that the increase of phosphorescence under the action of "N" rays takes an appreciable time whether to appear or to disappear. For, thanks to the storing-up of the "N" rays, the different parts of a mass of sulphide mutually reinforce their phosphorescence; but since, on the one hand, this reinforcing is progressive, as I have directly proved, and since, on the other hand, the stored-up provision is not immediately exhausted, the result is that when "N" rays are made to fall on phosphorescent calcium sulphide, their effect must increase slowly, and that when they are suppressed, their effect can only disappear slowly.[2]

Pebbles picked up at about four o'clock p.m., in a yard where they had been exposed to the sun, spontaneously emitted "N" rays; bringing them near a small mass of phosphorescent sulphide was sufficient to increase its luminosity. Fragments of calcareous stone, brick, etc., picked up in the same yard, produced analogous actions.

The activity of all these bodies still persisted after four days, without any sensible diminution. It is, however, necessary for the manifestation of such actions that the surface of these bodies should be quite dry; for we know that the thinnest layer of moisture is sufficient to arrest "N" rays. Vegetable earth was found to be inactive, doubtless on account of its moisture; pebbles taken from several centimetres underneath the surface of the soil were inactive, even after being dried.

The phenomena of the storing-up of "N" rays, which are the object of the present note, ought naturally to be compared with those of phosphorescence; yet they present a quite distinct feature, as I intend to show shortly.


  1. This sulphide was tightly packed into a slit cut into a sheet of cardboard 0.8 mm. thick; the width of the slit was 0.5 nd its length 15 mm. After exposure to sunlight, a small, luminous source is thus obtained, which is very sensitive to "N" rays.
  2. I repeat here that, as a rule, when experimenting with "N" rays, it is advantageous to replace the Auer burner by a Nernst lamp absorbing about 200 watts.