92 
MESSRS. W. DE LA RUE AND H. W. MULLER ON THE 
The value obtained for the point positive does not differ very greatly from the 
number of volts (8281) actually employed ; but that for the point negative is in the 
ratio of 1 ‘67 to 1. 
In calculating the force of attraction, it has been assumed that it was the upper 
surface of the paper which was charged to the highest negative or positive potential, 
according as the point was negative or positive, but it is possible that a zone of 
almost full potential was at some nearer distance from the metallic disc. It has been 
suggested that the whole mass of the paper serves as a conductor, resting on only a 
few points on the lower disc, and that the intervening film of air is the insulator ; 
against the correctness of this hypothesis is the fact that the adhesion is much stronger 
when the paper is made to insulate better by being dried. With paraffined paper 
black-leaded on the upper surface the adhesion was with point N 900 and with point 
P 400 grains, and it was almost inappreciable when the upper surface of the slip of 
paper had a disc of tin -foil pasted on it. 
There is no measurable adhesion when a spherical surface is substituted for the 
point : this was to be expected, for there is scarcely a visible glow, and consequently 
little transference of electricity before the jump of the spark. The only effect observed 
was that the slip of paper was attracted diagonally to both terminals, forming a bridge 
through which a minute current passed when the terminals were separated beyond the 
striking distance.*' 
When one of the terminals consists of a very fine platinum wire 0'002 inch diameter, 
and about 0 - 56 inch long, held in a holder like that used for holding needles in a mathe- 
matical instrument box, but adapted to go into our discharger, the wire takes up a straight, 
circular, or elliptical oscillation, the glow at the point forming a continuous line of 
light marking its course ; with the point positive the excursion is less than when 
negative, being with a potential of 8040 cells, and a distance between the terminals of 
0'32 inch, about 0‘375 inch, while with the point negative it is much more brilliant 
and about 0‘8 inch. By interposing a resistance of 4 megohms the statical discharge 
takes place from the extremity of the wire, frequently producing a beautiful and 
brilliant figure by the apparent crossing and interlacing of the bright lines of discharge 
from different points in the path of the oscillating wire ; these occur at such short 
intervals that the discharge looks like a persistent pattern of intricate engine -turning. 
By approaching the wire cautiously it is generally possible to cause the end of it to 
fuse into a minute globule, and the discharge then becomes much more striking. 
With 4 megohms’ resistance the static spark is longest and brightest when the wire is 
negative ; if the wire is very straight the oscillations take place in- a cycloidal curve in 
a vertical plane, the discharge occurring at equal distances from the middle of the path 
as the minute globule at the end of the wire attains the limit of the greatest discharge 
from either side, so that two streaks of light are seen continuously ; if the wire is slightly 
* Professor Stokes, to whom we communicated these results, has favoured us with some remarks, 
which we insert with his permission in Note A. 
