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the expected unequal impressions, two sensibly identical images were obtained. I believe this failure, unique, be it remarked, to be due to an insufficient regulation of the spark, which, doubtless, was not sensitive. Fig. 6 is a photo-engraved reproduction of the prints obtained with and without “N” rays issuing from a Nernst lamp.

Fig. 7, similarly, shows the result of an experiment with “N” rays, produced by two large files.

Though the photogravures are far from rendering in a satisfactory manner the aspect of the originals, they nevertheless show the influence of “N” rays on a photographic impression.

I give further (Figs. 8 and 9) the reproduction of photographs, showing that “N” rays, issuing from a Crooke's tube, are polarized.

These photographs date from the month of April, 1903. They were not obtained by the method of reiterated alternation of exposure, as this method is difficult to apply to this case; but the experiments have been repeated a great number of times with the most minute

precautions, and the constancy of the results is an absolute guarantee of their worth.

From my communication of May 11, 1903, and from what precedes, it is clear that, from the beginning of my researches on “N” rays, I had succeeded in recording their action on the spark by an objective method.

On a New Species of "NRays (February 29,

1904). Observations made during a very complex experiment, which I owe to Dr. Th. Guidloz, led me to suspect the existence of a variety of “N”rays, which, instead of increasing, on the contrary, diminished the glow of a feeble luminous source. I undertook to search for rays of this type amongst those emitted by a Nernst lamp. While previously studying the spectrum of this emission, produced by an aluminium prism, I had not met with such radiations. I consequently thought that there were reasons for studying anew, and still more minutely, the feebly deviated part of the spectrum. On

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exploring this region, by means of a narrow slit filled with phosphorescent calcium sulphide, I ascertained, without any difficulty, that, in certain azimuths, the glow of the spark diminished under the action of the rays, and increased, on the contrary, when they were intercepted by a wet screen. These were, in fact. the looked-for radiations ; I will call them “N,” rays.

Although the aluminium prism of 27° 15' I used previously is suitable for these experiments, nevertheless, in order to increase the dispersion, I used an aluminium prism of 60°, and afterwards another of goo. With the help of the latter, I very carefully studied the feebly deviated part of the spectrum. The prism was arranged so that the angle of incidence was 20°; for each radiation, the deviation was measured and the refractive index deduced; then the wave-length was determined by means of a Brunner grating of 200 lines to the millimetre, by the process already described (see p. 57). The following table gives the numbers which result from this study, and were used for constructing the diagram (Fig. 10), in which

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