A. W. Wright — Cathode Rays and their Effects. 241 



through the metal. Their inner edges were 5*6 mm apart, and 

 they were parallel to the shorter dimension of the plate. On 

 one side of the copper plate was soldered a strip of thinner 

 sheet copper at right angles to the length of the slits, and about 

 three millimeters from their ends. One side of the strip was 

 turned up at right angles to the copper plate and formed a 

 ledge for the end of the sensitive plate to rest upon, and to 

 serve as a guide in placing it in position. The copper plate was 

 placed in a horizontal position beneath the vacuum-tube and 

 distant from it about one decimeter (97 mm ), the cathode being 

 carefully brought directly above the slits and pointing 

 towards them. In the lirst experiment, the results of which 

 are illustrated in PL "VII, the distance of the nearest part of the 

 tube was greater,' being 132 mm . The sensitized photographic 

 plate, wrapped in a single thickness of black paper, was placed 

 beneath the copper plate, with its upper end resting against 

 the guide ledge at the inner end of the slits, and inclined at 

 such an angle that its lower end was beyond the vertical line 

 through the outer end of the slits. The streams of cathode 

 rays passing through the slits were thus intercepted by the dry 

 plate, upon which they left their trace throughout its length. 

 The experiment was carried out as follows :— The dry-plate 

 was first placed so that the slits were at the middle of its upper 

 edge. One of the slits was covered with a strip of thick 

 copper plate and an exposure of 30 minutes made, after which 

 it was uncovered, the copper strip transferred to the other slit, 

 and a second exposure of equal length made. This was for the 

 purpose of fixing upon the plate the position of the cathode 

 stream from each slit uninfluenced by the presence of the 

 other. The sensitive plate was now moved along in its own 

 plane, both slits were uncovered, and a new exposure of 

 the same length as before was made. This was to detect 

 any repulsion such as occurs under similar circumstances 

 within a vacuum-tube. Finally the photographic plate was 

 moved in the opposite direction, bringing the slits over 

 a point nearly midway between the center and the edge, 

 and a powerful Jamin magnet so placed, that' if any effect 

 upon the cathode streams were produced, such as is seen 

 in a vacuum-tube, they would be deflected away from the 

 center of the plate. The consecutive positions of the slits rela- 

 tively to the plate are indicated by the numbers 1, 2, 3 in the 

 illustration, PI. VII. 



Development of this plate showed some interesting results. 

 Opposite each position of a slit is a trail extending nearly 

 across the length of the plate, of the same breadth as the slit 

 where the latter met the upper end of the plate, and spreading 

 out in a fan like shape at an angle of very nearly 15°. The 

 sides of each trail, near the origin, are well defined, and recti- 



Am. Jour. Sci.— Fourth Series, Vol. I, No. 3. — March, 1896. 

 16 



