542 Prof. J. J. Thomson on the Relation between the 



electrified hydrogen or oxygen atom moves more quickly under 

 equal electric intensities than a positively electrified one. 



The outside coatings of two Leyden jars, A, B (fig. 6), 

 were connected by a wire wound into a coil C. In this coil 

 an exhausted bulb was placed and a platinum wire fused into 

 the bulb ; this wire was connected with an electrometer. _ lne 

 inside coatings of the jar were connected with the terminals 

 of an induction-coil through the primary of which the alter- 

 nating current used for lighting the laboratory passed. This 

 caused an arc-discharge to pass be- Fig- 6 « 



tween the terminals of the induc- 

 tion-coil, and produced a potential 

 difference between the insides of the 

 jars. This potential difference can 

 be very greatly increased by direct- 

 ing a blast of air on the space 

 between the terminals of the in- 

 duction-coil, and so blowing out 

 the arc. If we now examine the electrical state of the 

 platinum wire in the bulb, we shall find that, when the blast 

 is on, the wire acquires a positive charge when placed near 

 the equator of the bulb (by the equator of the bulb we mean 

 the region inside the bulb adjacent to the coil which encircles 

 it) , and a negative charge when placed near the pole. If, 

 however, after the blast has been on for some time, it is 

 suddenly stopped and the arc allowed to pass between the 

 terminals of the induction-coil, the sign of the electrification 

 is reversed, the platinum wire now acquiring a positive charge 

 when placed at the pole of the bulb and a negative charge 

 when placed at the equator. Both these results are, I think, 

 explicable if we suppose that the negative atoms diffuse more 

 rapidly than the positive ones. For, take the case when the 

 arc is blown out. Here there is a great potential difference 

 between the electrodes, and the coil surrounding the bulb is 

 raised to a high potential. This causes a brush-discharge to start 

 from the glass into the rarefied gas in the bulb, the discharge 

 starting from the part of the glass nearest the coil, L e. from the 

 equator. If, now, the negative atoms travel faster through 

 the bulb than the positive, then, even though the same number 

 of the two kinds of atoms start from the glass, the negative 

 atoms will be in excess in the region remote from the origin 

 of the discharge, while near this origin the positive atoms will 

 be in excess : thus we shall have positive electrification at 

 the equator,, negative electrification at the poles. Let this go 

 on until a number of positive and negative atoms are dis- 

 persed through the bulb. Then stop the blast. This at once 



