260 DISCHARGE OF P:LECTRICITY. 



suddenly, but as it were feels its way. The gas tirst breaks down 

 along' the line where the eleetro -motive intensity is a niaximuiu, and a 

 small discharge takes place along this line. This discharge produces 

 a su])ply of dissociated molecules along which subsequent discharges 

 can pass with greater ease. Thus under tlie action of these electric 

 forces the gas is in a state of unstable equilibrium, since as soon as 

 any small discharge passes through it the gas becomes electrically 

 weaker and less able to resist sul)sequent discharges. When the gas 

 is in a magnetic held, the magnetic force acting on the discharge pro- 

 duces a mechanical force which displaces the molecules taking part in 

 the discharge from the line of maximum electric intensity, and thus 

 subsequent discharges do not find it any easier to pass along this line 

 in consequence of the passage of the previous one. There will not 

 therefore be the same instability in this case as in the one where no 

 magnetic force acted upon the gas. A confirmation of this view is, I 

 think, afforded by the appearance presented by the discharge when 

 the intensity of the magnetic held is reduced, so that the discharge 

 Just — but only jnst- — passes when the magnetic held is on. In this case 

 the discharge, instead of passing as a steady fixed ring, flickers about 

 the tube in a very undecided way. 



If the strength of the magnetic held is reduced still further, so that 

 the discharge passes with some ease, the bright ring which, when no 

 magnetic force is acting, is in one i)lane, is changed into a luminous 

 baud situated between two planes which intersect along a diameter ot 

 the bulb at right angles to the magnetic force. These planes are in- 

 clined at a considerable angle, one being above and the other below 

 the plane of the undisturbed ring. This displacement of the ring by 

 the magnetic force shows tliat it consists of currents circulating tan- 

 gentially round the ring. 



This action of a magnet on a discharge flowing at right angles to its 

 lines of force is not, however, the only remarkable effect produced by a 

 magnet on the discharge. Wlien the lines of magnetic force are along 

 the line of discharge, the action of the magnet is to facilitate the dis- 

 charge and not to retard it as in the former case. The first indication 

 Of this was ol)served when the jars were connected, as in {a) Fig. 1. 

 The earth connection being removed, in this case there is a glow from 

 the glass into the bulb, due to the re-distribution of the electricity 

 induced on the glass by the primary when it is at a high potential 

 before the s})ark passes. If the ])rimary is connected to earth by a 

 circuit with an air break in it, the intensity of the glow may be altered 

 at will by adjusting the length of the air break; when the air-space is 

 very small tliere is no glow; when it is long the glow is bright. The 

 bulb in which the discharge Avas to take place was placed on a piece of 

 ebonite over the i)ole of an electromagnet, and the air-space in the 

 earth connection of the primary was adjusted so that when the magnet 

 was ort' no glow was observed in the tube. When the nuiguet was on, 



