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The whole was in a perfectly dark room optically, and the eye was placed above the tube looking down. After the eyes had acquired a maximum sensitiveness by the total exclusion of light for ten to fifteen minutes, the Crookes bulb was set in operation and the space within the brass tube critically examined from above. The screen was unmistakably luminous to the eye and the windows were clearly located. Now the polished zinc was moved about in front of one of the openings, in the hope of detecting a variation of luminosity on the screen opposite this window. The result was at first disappointing; the position of maximum effect was certainly not that of 45°, as employed in the photographic experiments. In fact, very incon. sistent positions seemed to give the greater illumination through the window under attention. Finally it became quite obvious that the zinc had little to do with what was visible. In fact, on laying aside the metal I was able to light up brighter than ever the inside of the brass box by holding my hand in a suitable position in front of the window.

This experiment made certain by ocular demonstration that the human hand has by being placed in the path of the X-rays absorbed some sort of energy, by means of which it has acquired the property of emanating something capable of exciting fluorescence upon the screen. It remains now to demonstrate what effect these emanations will have upon a photographic plate as compared with those from the zinc, and Fig. 10 shows the result of a threeminute exposure with my hand only, placed opposite one of the windows, the tube resting upon a photographic plate in its usual protecting envelopes. A similar experiment was next tried (see Fig. 11) by holding a hand in front of each window, one of the latter being closed by a thin sheet of plate glass. It is obvious from the results obtained that the physiological rays emitted by the hands affect the plate through its protecting covers, but are unable easily to penetrate glass.

It is only a step now to produce a "physio-radiogram," and Fig. 12 is a reproduction of a record made by the secondary activity emanating from my own hand stimulated by a stream of Roentgen rays with an exposure of three minutes. The shadows are those of a cent, a gold finger-ring and a piece of aluminum about half a millimetre thick, and it is apparent that aluminum is somewhat translucent to these rays.

Although Guilloz' had made just such shadow radiographs with

Sagnac rays emanating from his hand, the visible fluorescence generated by the tube was not cut off by any opaque screen, and there is no reason for assuming that this light may not have played some part in his results. In the present experiments everything has been done in complete optical darkness.

I have been unable to find out if Guilloz's pictures were actually published, and so cannot compare his results in detail with my own. In connection with the present subject, my attention has been called by unpleasant personal experience to a very suggestive coincidence. The nature and pathology of X-ray dermatitis is, and has been from the first, surrounded with mystery. Much ingenious technical literature has been published in the medical journals all over the world for the last six years, with the result that to-day little is known about either the real cause, the nature, the proper method of preventing, or the best treatment of this most distressing and lingering affliction. A comparative history of many cases reveals many inconsistencies, followed by an increased sense of ignorance on the subject. The personal experience to which I refer suggests a possible step towards a better understanding of the phenomenon.

During a week in June, 1902, I occupied the Roentgen ray room as a sleeping apartment. At the end of this time an acute inflammation of the eyes and throat appeared, all symptoms of an ordinary cold or of any digestive disturbance being absent. At the end of the week referred to I left town and the inflammation gradually subsided during the next three or four days. For similar reasons I had occasion to sleep in the same room during the first week of the present month. At the end of that time my attention was painfully called to a recurrence of the symptoms observed a year ago. On ceasing to sleep in the room all trouble disappeared.

As I have never had any such experiences other than those referred to, it seems not too much to infer that the peculiar inflammatory condition may have been due to some action of the secondary emanations sent out by the walls and air of the room after the generation of X-rays had ceased. Continuous breathing of such "darkly phosphorescing" air might well account for the trouble in the throat and vocal chords. In the daytime the doors and windows were always more or less open, so that the air was continuously changing, and my eyes were protected considerably by glasses, through which neither the primary nor the secondary rays pass easily.

The inference seems fair that the recurrence of the inflammatory condition was not a mere coincidence, and that these secondary rays may be found to be of more importance than has been supposed.

1 Thompson, X-Rays, p. 70.

2 Thompson, X-Rays, p. 129.

BIBLIOGRAPHY.

3 Sagnac, Compte Rendus, 1897-98. Physique (7), xxii, 1901; pp. 493-563.

Sagnac, Annales de Chemie et de
Perrin, Compte Rendus, Vol. cxxiv,

P. 455. Townsend, J. S., Proc. Camb. Philos. Soc., 1900, x, pp. 217–226. 4 Guilloz, Compte Rendus, February, 1900.

UNIVERSITY OF PENNSYLVANIA,

RANDAL MORGAN LABORATORY OF PHYSICS,
May 15, 1903.

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ON THE DEPENDENCE OF WHAT APPARENTLY TAKES
PLACE IN NATURE UPON WHAT ACTUALLY
OCCURS IN THE UNIVERSE OF REAL EXIST-
ENCES.

BY G. JOHNSTONE STONEY, M.A., SC.D., F.R.S.
(Read April 3, 1903.)

CHAPTER I. INTRODUCTION.

Hitherto attempts to ascertain the events that are actually happening in the universe of real existences, and to ascertain what those existences are-in other words, the study of ontology-have been pursued almost exclusively from the standpoint of the metaphysician of the human mind. This mode of treatment has led to a few negative results which are chiefly of value by helping to dispel some popular errors, but it has established little that is positive, or that can be of service to the scientific student of nature. And yet investigations of Natural Science have been pushed in more than one direction into contact with problems of ontology, and are there brought to a stand owing to the different levels at which these two fields of investigation lie. Examples of this are met with in physiology, when we find our progress blocked on coming face to face with the problem as to what is the true nature of the interdependence between the thoughts of animals and changes in their brains; and generally throughout physics, when we make any attempt to penetrate to the causes of the events that occur. It appears, therefore, to be in an eminent degree desirable that an attempt shall be made to bring natural science and ontology into line by carrying on the ontological investigation from the standpoint of the scientific student of nature.

PROC. AMER. PHILOS. SOC. XLII. 173. H. PRINTED JUNE 6, 1903.

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