of Edinburgh, Session 1879 - 80 . 557 
connections reversed. The deflection in the table is the position 
of the wire-image immediately before the passing of the spark ; and 
the zero is its position after the spark had passed, and the Leyden 
jars of the Holtz machine had been discharged. These jars were 
found to contain a residual charge, but its existence had only a 
very slight effect upon the position of the wire-image. 
In the second series of observations, the arrangement differed 
only in this — That a spherical ball of “5 inch diameter was attached 
to the end of the rod. 
From the first series of observations* by taking the mean of the 
two opposite readings, we obtain the following results : — 
Point and Plate. 
Distance 
between Point 
and Plate. 
Electromotive 
force for Positive 
Discharge (1). 
Electromotive 
force for Negative 
discharge (2): 
Ratio of (1) 
to (2). 
\ inch 
76 -6 
67-1 
1-14 
1 inch 
8ff3 
76-2 
1-13 
2 inches 
102-3 
95-2 
1-07 
Thus the electromotive force for the positive discharge was always 
greater than for the negative} but the ratio approaches the more 
nearly to unity the greater the distance of the point from the large 
plate. Thus the difference in the electromotive forces appears to be 
due to the presence of the large uninsulated plate. The behaviour 
of the index showed that the discharge was not single, but consisted 
of a rapid succession of discharges* for it first attained a temporary 
maximum deflection and then a steady deflection slightly less than 
the maximum. The latter bn accbunt of its being capable of being 
observed with greater precision was the one recorded. The dis- 
charge was not silent, but accompanied with a slight hissing 
sound. 
From the second table, by taking the mean of the two opposite 
readings, we obtain the following results : — 
