156 
MB, W. CROOKES ON THE ILLUMINATION OE LINES OF 
not the same line of molecules which forms the curved hue c c. The action of the 
magnetic force is to twist the whole of the trajectories of the molecules round in a 
direction at an angle to their normal path, and to a greater extent as they are nearer 
the magnet, the direction of twist being that of the electric current passing round 
the electro-magnet. The line c c is therefore not the line b b twisted out of its place, 
but is another line, e e, which is bent round from e to c by the magnet, the line b b 
passing away somewhat in the direction ff. 
552. A long glass tube, fig. 18, was made with a flat fluorescent screen running along 
its whole length ; this screen had 12 vertical glass pegs fixed into it at intervals of 
25 millims. apart. The negative pole of the coil was not quite in the axis of the tube, 
but a little on one side, so as to cast sloping shadows of the pegs across the fluorescent 
plate. When the magnet was placed in the position S N, but not excited, the 
shadows fell as at 1, 2, 3 ; but when the current was turned on the shadows twisted 
round to 1/ 2' 3', shadow No. 1 bending in at a as well as out at b, and the others 
acting in a similar way to a less extent. 
A 
-1—3—L4—5— H~l~H-TA / 
Elevation. 
Fig. 18. 
A 
l'S 12' 2 3' 3 
Plan. 
553. When the north pole of the magnet is placed vertically under one of the pegs, 
as at fig. 18, A, the shadow is twisted from position 1 to 1'. 
554. These phenomena of magnetic deflection are obtained with permanent magnets 
as well as with electro-magnets. A copper wire helix without the iron core acts like 
an electro-magnet, but fainter, when an electric current is passed through it. The 
shadows experimented with in the tubes and bulbs already described are easily 
deflected by bringing a magnet near. 
ALTERATION OE MOLECULAR VELOCITY.—LAW OF MAGNETIC DEFLECTION. 
555. It has been shown (546) that the position of the edge of the shadow is affected 
by varying the magnetic power used to deflect it. It became of interest to see if 
by keeping the magnetic power constant, the position of the edge of the shadow 
could be altered by any circumstance affecting the intensity of the spark, such as 
intercalating a Leyden jar in the circuit, or screwing the contact breaker one way or 
