TROWBRIDGE. — ELECTRICAL DISCHARGES. 445 



inch in thickness, and in another case by a sheet of glass about half an inch 

 in thickness. A powerful brush discharge was seen in the dark room to 

 pass from the thin bulb of the tube to the insulator which covered the 

 plates, and on developing the plates they were found to be covered with 

 star-like clusters surrounded by nebulous patches. It was evident that 

 the brush discharge had produced discharges at the surface of the dry 

 plate, even through plates of glass half an inch in thickness. Moreover 

 tliere was a general darkening of the surface of the plate which indicated 

 the action of the X-rays. No metallic objects could be placed upon the 

 dry plates, for a powerful spark immediately passed to them and punc- 

 tured tlie tubes. The darkening, however, was apparently diminished 

 under strips of glass, although the effect of the brush discharge masked 

 the effect of the X-rays. 



Before the straight tube was exhausted powerful brush discharges 

 were given off at the ends of the tube. When the tube was exhausted 

 these brushes were much diminished and were replaced by a powerful 

 brush, which came off from the straight wire through the bulb of the tube 

 and speedily punctured the latter when any object, even an insulator, 

 was brought within six inches of the bulb. The most interesting result 

 obtained with this form of tube was the production of the so called X- 

 ray burn by means of the brush discharge from its bulb. When the back 

 of the hand was exposed to this brush discharge, which assumed a peculiar 

 forked nature in the dark room, a peculiar prickling sensation was ex- 

 perienced, and all the symptoms of the well known X-ray burn developed. 

 The skin when examined under a microscope exhibited an appearance 

 similar to that shown by the photographic plate. There were centres of 

 inflammation surrounded by regions of lesser degrees of burn. It seems 

 evident that the so called X-ray burn is due to an electrification, — a dis- 

 charge at the surface of the skin, — and this electrification may or may 

 not be accompanied by the X-rays. The first form of tube was then 

 abandoned, and a straight wire tube alone (Fig. 2) was employed. Simi- 

 lar results were obtained with this tube. It was significant that the 

 whole interior of this tube fluoresced brilliantly when it formed part of a 

 circuit through which a disruptive discharge passed. This latter form 

 of tube was replaced by that represented in Figure 3. A side ending in 

 a thin bulb was added to the straight wire tube. The same phenomenon 

 was exhibited by this tube : in addition, a brilliant fluorescence filled the 

 side tube, which appeared to flow in or flow out of the narrow tube 

 which ended in the small bulb. One is reminded by this phenomenon of 

 Poynting's hypothesis of the flow of energy into a wire. This form of 



