Sept. 4, 1879] 



NATURE 



437 



Radiant Matter is deflected by a Magnet 



I now pass to another property of radiant matter. This long 

 glass tube (Fig. 14), is very highly exhausted ; it has a negative pole 

 at one end (a) and a long phosphorescent screen {b, c) down the 

 centre of the tube. In front of the negative pole is a plate of 

 mica {(5, d) with a hole (e) in it, and the result is, when I turn 

 on the current, a line of phosphorescent light (e, f) is projected 

 along the whole length of the tube. I now place beneath the 

 tube a powerful horse-shoe magnet : observe how the line of light 

 (e, g) becomes curved under the magnetic influence waving about 

 like a flexible wand as I move the magnet to and fro. 



This action of the magnet is very curious, and if carefully 

 followed up will elucidate other properties of radiant matter. 

 Here (Fig. 15) is an exactly similar tube, but having at one end 

 a small potash tube, which if heated will slightly injure the 



vacuum. I turn on the inducti in current, and you see the ray 

 of radiant matter tracing its trajectory in a curved line along tlie 

 screen, under the influence of the horse-shoe magnet beneath. 

 Observe the shape of the curve. The molecules shot from the 

 negative pole may be likened to a discharge of iron bullets from 

 a mitrailleuse, and the magnet beneath will represent the earth 

 curving the trajectory of the shot by gravitation. Here on this 

 luminous screen you see the curved trajectory of the shot accu- 

 rately traced. Now suppose the deflecting force to remain con- 

 stant, the curve traced l^y the projectile varies with the velocity. 

 If I put more powder in the gun the velocity will be greater and 

 the trajectory flatter, and if I interpose a denser resisting medium 

 between the gun and the target, I diminish the velocity of the 

 shot, and thereby cause it to move in a greater curve and come 

 to the ground sooner. I cannot well increase before you the 

 velocity of my stream of radiant molecules by putting more 



powder in my battery, but I will try and make them sufier 

 greater resistance in their flight from one end of the tube to the 

 other. I heat the caustic potash with a spirit-lamp and so throw 

 in a trace more gas. Instantly the stream of radiant matter 

 responds. Its velocity is impeded, the magnetism has longer 

 time on which to act on the individual molecules, the trajectory 

 gets more and more curved, until, instead of shooting nearly to 

 the end of tli£ tube, my molecular bullets fall to the bottom 

 before they have got more than half-way. 



It is of great interest to ascertain whether the law governing 

 the magnetic deflection of the trajectory of radiant matter is the 

 same as has been found to hold good at a lower vacuum. The 

 experiments I have just shown you were with a very high vacuum. 

 Here is a tube with a low vacuum (Fig. 16). When I turn on 

 the induction spark, it passes as a narrow line of violet light 



Fig. 16. 



joining the two poles. Underneath I have a powerful electro- 

 magnet. I make contact with the magnet, and the line of light 

 dips in the centre towards the magnet. 1 reverse the poles, and 

 the line is driven up to the top of the tube. Notice the differ- 

 ence between the two phenomena. Here the action is temporary. 

 The dip takes place under the magnetic influence ; the line of 

 discharge then rises and pursues its path to the positive.pole. In 

 the high exhaustion, however, after the stream of radiant matter 

 had dipped to the magnet, it did not recover itself, but continued 

 its path in the altered direction. 



By means of this little wheel, skilfully constructed by Mr. 

 Gimingham, I am able to show the magnetic deflection in the 

 electric lantern. The apparatus is shown in this diagram 

 (Fig. 17) The negative pole (a,b) is in the form of a very 

 shallow cup. In front of the cup is a mica screen (<-, d), wide 

 enough to mtercept the radiant matter coming from the negative 



pole. Behind this screen is a mica wheel {e, f) with a series ot 

 vanes, making a sort of paddle-wheel. So arranged, the mole 

 cular rays from the pole a b will be cut off' from the wheel, and 

 will not produce any movement. I now put a magnet, g, over 

 the tube, so as to deflect the stream over or under the obstacle 

 c, d, and the result will be rapid motion in one or the other 

 direction, according to the way the magnet is turned. I throw 

 the image of the apparatus on the screen. The spiral lines 

 painted on the wheel show which way it turns. I arrange the 

 magnet to draw the molecular stream so as to beat against the 

 upper vanes, and tlie wheel revolves rapidly as if it were an over- 

 shot water-wheel. I turn the magnet so as to drive the radiant 



Fig. 17, 



matter underneath ; the wheel slackens speed, stops, and then 

 begins to rotate the other way, like an under-shot water-wheel. 

 This can be repeated as often as I reverse the position of the 

 magnet. '*"•■ v*i 



I have mentioned that the molecules of the radiant matter 

 discharged from the negative pole are negatively electrified. It 

 is probable that their velocity is owing to the mutual repulsion 

 between the similarly electrified pole and the molecules. In less 

 high vacua, such as you saw a few minutes ago (Fig. 16), the 

 discharge passes from one pole to another, carrying an electric 

 current, as if it were a flexible wire. Now it is of great interest 



