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On the Property of emitting “N” Rays, which is
conferred on Certain Bodies by Compression,
Professor A. Charpentier kindly undertook to keep me informed with regard to the progress of certain researches of a physiological nature which he is conducting in connection with “N” rays, unpublished researches which (note 11) promise highly interesting results. These experiments led me to the idea of examining whether certain bodies did not acquire, by compression, the property of emitting “N” rays. For this purpose I compressed, by means of a carpenter's press, bits of wood, glass, rubber, etc., and I immediately observed that these bodies had in fact become, during the compression, sources of “N” rays; brought near a mass of phosphorescent calcium sulphide, they increased its luminosity; and they can also be
used for repeating the experiments which show the strengthening of the action on the retina by light when “N” rays are acting simultaneously on the eye.
These last experiments may be made in a very simple manner. The shutters of a room should be closed so as to leave just enough light for a white surface standing out on a dark background-for instance, the dial of a clockto appear, before an observer 4 or 5 metres distant, like a grey patch with ill-defined contours. If a cane stick placed before the eyes is bent, the grey surface is seen to whiten ; if the cane is allowed to straighten, the surface grows dark again. Instead of the cane, a slip of plate-glass can be used. This is bent either with the press employed in lectures for showing the doubly refractive property of glass acquired by flexure, or simply with the hands. With a suitable amount of light, which may be obtained after a few trials, these phenomena are easily visible. They are not instantaneous, as I have already explained. It is of the utmost importance that this retardation be taken into account when one wishes to study these phenomena ;
to this may doubtless be ascribed the fact that they have remained so long undetected.
I was then led to ask myself whether bodies which are themselves in a state of strained internal equilibrium would not emit “N” rays. That they do so is indeed confirmed by experiment. Rupert's drops, hardened steel, hammer-hardened brass, melted sulphur of crystalline structure, etc., are spontaneous and permanent sources of “N” rays. One can, for instance, repeat the experiments with the clock dial, employing, instead of a compressed body, a hardened steel tool, such as a chisel or file, or even a pocket-knife, without in any way bending or compressing them; similarly, bringing near to a small mass of phosphorescent calcium sulphide a knife-blade or bit of unannealed glass is sufficient to increase the phosphorescence. Non-hardened steel is without action ; a chisel which is successively hardened and softened in turn is active when hard and inactive when the temper is taken out of it. These actions traverse, without any notable weakening, a plate of aluminium 1.5 cm. thick, an oak board 3 cms. thick, black paper, etc.
The emission of “N” rays by tempered steel seems to last indefinitely. Some lathetools and a stamp for leather of the 18th century, which have been preserved in my family, and have certainly not been rehardened since the date of their manufacture, emit “N” rays like freshly tempered steel. A knife, found in a Gallo-Roman tomb, situated in the district of Craincourt (Lorraine), and dating from the Merovingian epoch, as is attested by the objects found there (glass and earthenware jars, fibulæ, belt-buckles, swords of the kind called scramasax, etc.), emits “N” rays just like a modern knife. These rays originate exclusively from the blade; a test with a file showed that the blade alone is tempered, and that the tailpiece intended to be fixed in a handle is not tempered.
The emission of “N” rays by this steel blade has thus persisted for more than twelve centuries, and does not appear to have abated.
1 The primitive Gauls do not appear to have known steel, for, from Polybius' account, their iron swords did not stab, and bent in combat at the very first blows. The knife alluded to here is of Gallo-Roman origin, and the Gallo-Romans had doubtless learnt from the Romans the art of making and tempering steel.
The spontaneity and the indefinite duration of the emission by steel suggests the idea of assimilating it to the radiant properties of uranium, discovered by M. H. Becquerel, properties which the bodies since discovered by M. and Mme. Curie, viz. radium, polonium, etc., exhibit with so much intensity. Nevertheless, “N” rays are certainly spectrum radiations; they are emitted by the same sources as spectrum radiations; they are reflected and polarized, and possess well-defined wavelengths, which I have measured. The energy which their emission represents is most likely borrowed from the potential energy corresponding to the strained state of tempered steel ; this expenditure is doubtless very slight, since the effects of the “N” rays are likewise slight, which explains the apparently unlimited duration of the emission.
An iron plate, bent so as to impress on it a permanent deformation, emits “N” rays ; but the emission ceases after a few minutes. A block of aluminium, fresh-hammered, behaves in an analogous manner ; but the time of emission is even shorter. In these two cases the