A. W. Wright — Cathode Bays and their Effects. 243 



to be volatilized with great facility when used as a cathode. 

 It was thought that the passage of the cathode rays through it 

 would cause the liberation of the metal in their path, in the 

 same manner as within the tube, and thus cause them again to 

 become susceptible to mutual 'repulsion, and to deviation by a 

 magnet. 



This expectation appeared to be justified by the character 

 of the trails upon the developed photographic plate, although 

 the changes were not great. The angles were determined by 

 measurement, in most cases by pricking the outlines of the 

 streams with a fine needle on a positive print, and then tracing 

 the lines of direction of the perforations with a straight-edge 

 upon paper. The angular spread of the streams was greater 

 than in the previous experiment, being now about 18°. The 

 effect of the magnet was shown by a small deviation, in the 

 direction expected. The measurements of its amount were 

 difficult to make, but all agreed in showing a positive effect, of 

 something like half a degree. The mutual repulsion of the two 

 streams was also clearly shown, the angle between the axes of 

 the pencils being increased a little more than half a degree. It 

 was also evidenced by the fact that when the axes were pro- 

 longed they were found to meet at a point nearer the slits than 

 those of the pencils produced singly. 



A third experiment, in which a sheet of aluminium, 0*26 mm 

 in thickness, replaced the gold leaf, was now made under the 

 same conditions as before. As this metal, though readily per- 

 meable by the cathode rays, is very slightly affected when used 

 as an electrode, it was not to be expected that it would modify 

 the stream of cathode rays to the same extent as the gold. 

 This the developed plate confirmed. The magnetic deviation 

 could not be detected with certainty, but the mutual repulsion 

 of the two streams was somewhat greater than before. 



An attempt to discover the point of departure of the rays 

 was made by tracing the axes of the trails or pencils until they 

 met upon the plot. In the case of the first two experiments, 

 they were found to come together at a point very near the cen- 

 ter of the spherical body of the vacuum-tube, thus indicating 

 that they left the surface of the glass nearly normally. The 

 third case showed the point of meeting nearer the cathode, 

 but the results of the three pairs of pencils varied much from 

 each other. 



While it is doubtless premature, in the present state of our 

 knowledge to formulate a conclusion as to the nature of the 

 rays which produce these remarkable results, we may derive 

 some useful suggestions from a consideration of the circum- 

 stances of their production. If the cause of the excitation is an 

 ordinary induction coil, the resistance of the circuit of the second- 

 ary is so great that the oscillations in this circuit at each opening 



