the black area be so large? If the electricity and vacuum have nothing to do with it, why should not the halos appear when photographs are taken of flames and other sources of light in the absence of mist and dust? In order to answer questions which will perhaps be proposed, let it be stated that there was no visible dust nor moisture in the room, the photograph being taken early in the evening and at a time when the Hall was not in use. The halos were not apparent except when reproduced by a photograph. The lamps had the usual carbon filaments hanging so that the several filaments were in different planes, and they were of 16 candle power and were connected in parallel circuit, the average E. M. F. being about 110 volts. The lamps were fed by the Edison direct current dynamos. The festoon shown, is one of a dozen or more which were suspended between the columns rising from the gallery and supporting the roof and were hung about forty feet from the floor. The hall was further illuminated by a huge electrolier pendant from the centre of the ceiling. These details were obtained from Mr. Hammer, who planned the installation. 141. ANÆSTHETIC PROPERTIES OF X-RAYS.—Tesla reported that he and his assistants tested the action of the rays upon the human system, and found that upon continued impact and penetration of the head by very powerful radiations, strange effects were noticed. He was sure that from this cause a tendency to sleep occurred (§ 84, at end), and the faculties were benumbed. He said that time seemed to pass quickly. The general effect was of a soothing nature, and the top of the head seemed to feel warm under the influence of the rays. Incidentally, he noticed, as he stated, “When working with highly strained bulbs, I frequently experienced a sudden and sometimes even painful shock in the eye. Such shocks may occur so often that the eye gets inflamed, and one cannot be considered cautious if he abstains from watching the bulb too closely.” The author calls to mind the reports in the daily press that Edison also noticed that the eyes were in some way sensitive to the rays. The eye, it was reported, became fatigued at the time, and yet later, objects could be more easily distinguished. In this connection, it should be remembered that there are not only cathode rays, X-rays, etc., but the electric force that Lenard spoke of in the neighborhood of the discharge tube, and in testing the effects upon the eyes, of course, the precaution should be taken to determine whether cathode rays, X-rays or the electric sparks are answerable for the peculiar effects. Roentgen reasoned, § 84, that the eyes were not sensitive, but the rays, in his case, were not strong enough to travel 40 to 60 feet, as in Tesla’s experiments, but only 2 m. (about 7 ft.).