584 Professor J. J. Thomson [March 22^ 



up to the walls of the tube, and was several centimetres thick, traces 

 of the positive column could be detected in the neighbourhood of 

 the anode. I will first take the case where the tube was filled with 

 air. Special precautions were taken to free the air from hydrogen ; it 

 was carefully dried, and a subsidiary discharge-tube, 

 having a cathode made of the liquid alloy of sodium and 

 potassium, was fused on to the main tube. When the dis- 

 charge passes from such a cathode it absorbs hydrogen. 

 The discharge was sent through this tube at the lowest 

 pressure at which enough light was produced in the gas 

 to give a visible spectrum, until the hydrogen lines dis- 

 appeared and the only lines visible were those of nitrogen 

 and mercury vapour. This pressure was a little higher 

 than that used for the investigation of the positive rays, 

 but a pump or two was sufficient to bring the pressure 

 ••; down to this value. The appearance of the phosphor- 



FiG. 6. escence on the screen when the rays were deflected by 

 magnetic and electric forces separately and conjointly 

 is shown in Fig. 6. 



The deflection under magnetic force alone is indicated by vertical 

 shading, under electric force alone by horizontal shading, and under 

 the two combined by cross shading. 



The spot of phosphorescence is drawn out into a band on either 

 side of its original position. The upper portion, which is very much 

 the brighter, is deflected in the direction which indicates that the 

 phosphorescence is produced by rays having a positive charge ; the 

 lower portion (indicated by dots in the figure), which though faint is 

 quite perceptible on the willemite screen, is deflected as if the rays 

 carried a negative charge. The length of the lower portion is some- 

 what shorter than that of the upper one, but is quite comparable with 

 it. The intensity of the luminosity in the upper portion is at these 

 pressures quite continuous ; no abrupt variations such as would show 

 themselves as bright patches could be detected, although, as will be 

 seen later on, these make their appearance at lower pressures. Con- 

 sidering; for the present the upper portion, the straightness of the edges 

 shows that the velocity of the rays is approximately constant, while 



the values of — range from zero at the undeflected portion to the 

 value approximately equal to 10^ at the top of the deflected band. 

 This value of — is equal to that for a charged hydrogen atom, and, 

 moreover, there was no specially great luminosity in the positions 

 corresponding to — = and ^-, the values for rays carried by nitro- 

 gen or oxygen atoms, though these places were carefully scrutinised. 

 As hydrogen when present as an impurity in the tube has a tendency 



