Mad Line for producing High Tension Electricity. 185 



re-united at the sparking point. The double wire is bent into oppo- 

 sing bends and angles to show the repellent action of the radial 

 emanations from the wires. The resting places of the dust are very 

 beautifully shown by the darkened spaces in this figure. 



No. 15 was produced in the same manner as the preceding, but on 

 glass instead of card. As the dust is so very easily moved on glass, 

 only one coil was used, and it is remarkable that the dispersive effect 

 exhibited by the double positive wires is actually greater than that 

 of the spark itself. It will be seen that the dark impress of the wire 

 is more marked upon the glass than upon the card. It will be ob- 

 served also that there is a very peculiar dark band lying outside of 

 each wire and running parallel with it, and that each of these bands 

 merges in a dark patch lying on each side of the sparking point. 

 These bands and patches may be assumed to represent places where 

 the dispersive force is considerably subdued. 



No. 16 is a transverse section of battery discharges showing the de- 

 flections of the circular lines produced by the interference of ' six 

 glass tubes 2^ inches long and f inch in diameter, erected on the 

 dust plate at equal distances from the centre and from each other. 

 It will be observed that the lines are not obliterated behind the tubes 

 and that curious new curves are developed. 



No. 17 shows similar effects produced by heavier discharges on a 

 more thickly covered dust plate. In this case it will be seen that 

 the circular outline of the figure is changed by the operation from 

 a circular to a twelve-sided form. A blunted angle is thrown out 

 opposite each glass tube and another midway between every two. 



No. 18 shows another dust plate similarly treated, but more lightly 

 covered and without the glass tubes, instead of which two flat screens 

 of cardboard, 3 inches high and 2 inches wide, were fixed perpen- 

 dicularly on opposite sides of the centre. In this case, although the 

 lines curve inwards behind the screens, they gradually die out 

 towards the centre and leave the middle portion undisturbed, but by 

 reducing the height of the screens to the level of the sparking point 

 the whole sheltered space became wholly filled up with lines as in the 

 two previous cases. 



No. 19 shows the effect of inverting two wine glasses upon the 

 dust plate so as to cover two circular patches of the dust and protect 

 them from the action of the air. In this case no lines were found 

 within the glasses. 



No. 20 shows a stained figure remaining on the card after the dust 

 was shaken off. Although there are some small portions where the 

 stain has failed to take effect, the figure is, upon the whole, preserved 

 with remarkable accuracy. 



No. 21 is another example of a stained figure in which some of the 

 circular lines are discernible. 



