http://www.rexresearch.com/blondlot/nrays.htm#18
Scientific American (October 14, 1905), p. 299 "Photographic Records of the Action of N-Rays" The much discussed problem of the existence of N rays could be settled only by an objective demonstration of their effects. As these rays exert no immediate action on photographic plates, Prof. Blondlot some time ago endeavored to obtain indirect photographic records, by taking a view of the same spark first without N rays, and afterward with N rays. In the latter case a more intense impression on the photographic plate was observed. Opponents of the French scientist contended that the electric sparks were not of sufficient constancy to warrant him drawing any definite conclusions from these experiments. Prof. Blondlot therefore continued his efforts in this direction, and in a memoir published in a recent issue of the Revue Generale des Sciences describes a few further experiments where every care has been takes to avoid any uncertainty. These experiments really demonstrate the objective existence of the radiations. The process used was practically the same as that employed previously, but for a telephone inserted in the secondary circuit of the induction coil. The assistant, by keeping the telephone receiver close to his ear, was in a position to check the regularity of the spark throughout the duration of the experiments. If the spark was extinguished owing to an excessive distance of the points, the sound in the telephone was also discontinued. If, on the contrary, the points touched each other, the sound became much more intense. Any irregularities in the spark might thus be detected, and if any were observed during a photographic experiment, the photographs were rejected. In a series of 35 experiments carried out with every care, 23 tests showed a most striking difference between the images obtained with and without N rays, while 8 tests gave a rather noticeable contrast, and 4 tests a contrast still visible though less marked. All the plates did show the action of N rays, and if the difference between the two photographic impression was not always of the same intensity, this must be ascribed to the impossibility of obtaining an absolutely exact regulation of the small spark. It is of great importance that exceedingly feeble sparks should be employed, the brilliancy of which be little more than the minimum luminous intensity capable of producing some impression on the plate. Under these conditions a small variation in luminous intensity will result in a great variation in the intensity of the photographic image, while in the case of a stronger illumination only a very small variation is obtained. In the experiments referred to, the N rays were produced by a Nernst lamp enclosed in a sheet-metal lantern. The N rays traversed successively an aluminum foil constituting the front wall of the latter, a pinewood plank 2 cm in thickness, another aluminum foil, an aluminum lens, a zinc foil, a piece of whitewood 2 cm in thickness, an aluminum foil, constituting an electric screen to protect the spark, and finally the wall of the pasteboard box inclosing the spark. With all these experiments one second or more has been allowed for the total duration of the exposure made without N rays so as to make sure that this exposure was somewhat longer than the other. Instead of simply taking two successive exposures with and without N rays, another method, consisting in cross-wise fractional photography, has been chosen in some instances. The exposure with N rays was made either before or after the other, and the experiments were varied in many other ways. Metal screens were used so as to eliminate any disturbances likely to be produced by electrical influence. Checking experiments were made, from time to time either by withdrawing the moist paper or by moistening it with salt water, when equivalent images were obtained in each case. These experiments seem to be free from any objection. While the results practically agree with those obtained in connection with former researches, the following interesting fact was discovered incidentally: If N rays be made to strike the primary spark of a Hertz oscillator, the secondary spark will decrease in brilliancy. This shows that N rays modify the electric phenomenon itself, and the intimate alteration of the spark is doubtless the cause for which the photographic experiments on the action of N rays is used as illuminant, whereas no result is obtained with other sources of light.
