# "N" Rays/On the Strengthening Action of a Beam of Light on the Eyes, When the Beam is Accompanied by "N" Rays

On the Strengthening Action of a Beam of Light on the Eyes, when the Beam is accompanied by "N" Rays (November 23, 1903).
While studying the storing-up of "N" rays by different bodies, I had occasion to observe an unexpected phenomenon. My eyes were fixed on a small slip of paper, dimly lighted, distant about i metre from me; a brick, one of whose faces had been sun-exposed, having been brought near laterally to the luminous pencil, with its sun-exposed face turned towards me, and a few decimetres distant from my eyes, I saw the slip assume a heightened glow; when the brick was removed, or when its non-exposed face was turned towards me, the paper grew ​darker. To remove all possibility of illusion, I arranged permanently a box closed by a cover and wrapped in black paper; in this completely enclosed box the brick was placed, and, in this manner, the dark background on which the slip stood out remained rigorously invariable, but the observed effect remained the same. The experiment can be varied in different ways. For instance, the laboratory shutters being almost closed, and the dial of the clock fixed to a wall which was just sufficiently lighted for the dial, at a distance of 4 metres, to be just perceived as a grey patch with no defined contour, if the observer, without changing his place, directs towards his eyes the "N" rays emitted by a previously exposed brick or pebble, he sees the dial whiten; he can trace distinctly its circular contour, and even succeed in seeing the hands. When the "N" rays are suppressed, the dial again grows dark. Neither the production nor the cessation of the phenomenon are instantaneous.
As in these experiments the luminous object is placed very far away from the source of "N" rays, and as, on the other hand, in order that ​the experiment may succeed, the rays must be directed, not towards the object, but towards the eye, there can be no question here of an increase in emission of a luminous body influenced by "N" rays, but indeed of a strengthening of the effect upon the eye, due to the "N" rays which are superposed on the luminous rays.
This fact astonished me all the more because, since the slightest film of water arrests "N" rays, it seemed unlikely that they could penetrate into the eye, whose humours contain more than 98.6 per cent. of water (Lohmeyer). The small quantity of salt contained in these humours must have rendered them transparent to "N" rays. But, then, in all probability, salt water must itself be transparent. Experiment shows that this is the case, for while a sheet of wet paper completely arrests "N" rays, a vase of Bohemian glass, 4 cms. in diameter, filled with salt water and placed in their path, lets them pass without sensible weakening. A very small quantity of sodium chloride is sufficient to render water transparent. What is more, salt water is capable of storing-up "N" rays, and ​in the above-described experiments the brick can be replaced by a vase of thin glass, filled with salt water, and previously exposed to the sun's rays; the effect is very marked. It is certainly due to the salt water, for the empty vase is without effect. This is a unique example of a phosphorescence phenomenon in a liquid body. It is true that the wave-lengths of "N" rays are very different from those of luminous rays, as results from measurements which it is my intention to describe very soon.
The eye of an ox, killed the day before, rid of its muscles and the tissues adhering to the sclerotic, proved to be transparent to "N" rays in all directions, and became itself active by sun-exposure; it is the storing-up of the "N" rays by the media of the eye which causes the retardation observed in the appearance and cessation of the phenomena which are the subject of the present note.
Sea-water and the stones exposed to solar radiation store up "N" rays which they afterwards restore. Possibly these phenomena play some hitherto unperceived part in certain terrestrial phenomena. Perhaps, also, "N" rays ​are not without influence on certain phenomena of animal and vegetable life.
The following are further observations concerning the strengthening action of "N" rays on luminous rays.
It is sufficient for the production of the phenomenon that the "N" rays reach the eye, no matter how, even laterally. This seems to indicate that the observer's eye behaves like an accumulator of "N" rays, and that it is these rays accumulated in the media of the eye which act on the retina, jointly with luminous rays.
It matters little whether in these experiments the rays are emitted by a body previously exposed to the sun, or are primary rays, produced for instance by a Nernst lamp.
Sodium hyposulphite, whether solid or dissolved in water, constitutes a powerful accumulator of "N" rays.