44 
PROFESSOR B. SANDERSON ON THE ELECTROMOTIVE 
variation gradually changed its character just as it does when mechanical excitations 
follow each other at short intervals. In a leaf of which the cross difference was, at 
the beginning of the experiment, abnormal, and which was excited 58 times in succes¬ 
sion in half an hour, the variation being observed alternately with the electrometer and 
galvanometer, the cross difference changed sign from — O'OOQ D. to -f-0’005 D. The 
mean difference and variation were in three successive periods as follows :—- 
1st period .... 
2nd period . . . 
3rd period .... 
Cross difference. 
Galvanometer. 
Electrometer. 
-0-0023 D. 
0 
+ 0-0036 D. 
-40-8 +137 
-51-0 0 
-61-4 0 
-29-8 +1-8 
-23-2 0 
-21-0 0 
In another similar experiment the cross difference changed, in a series of 32 exci¬ 
tations, from — 0*011 D. to +0'01 D., the second phase (positive deflection) diminished 
from +210 scale to +90 scale, while the first phase (negative) increased from —15 to 
—220. (6) When (3) was repeated with the difference that the lengths of wire were 
respectively 3 feet and 5 feet, instead of 1 foot and 2 feet in two series a and 6, so that 
the currents conducted through the leaf were, in series a, only sufficiently strong to 
produce the effect (2), viz. : a single positive deflection, whereas in series b they were 
sufficient to give rise to an excitation, it was observed that in series a the electrical 
relation between the upper and under surface remained unaltered, but that in series b 
the diphasic variation was followed by an after effect which subsided with the usual 
increase of the cross difference already described and exemplified. 
The preceding facts may be summed up as follows :—The closing of a voltaic current 
directed from the upper to the under surface of the leaf of Dionsea produces different 
effects according to its strength. Very weak currents give rise to feeble polarization. 
Currents of moderate strength produce a transitory increase of the cross difference, 
that is, make the under surface more positive to the upper surface than it was before. 
Strong currents produce this transitory increase of the cross difference, but, in 
addition, produce an excitation which is followed by a lasting increase of the cross 
difference. In the successive deflections observed, these two effects are summed ; so 
that the negative phase is diminished and the positive phase increased. 
The explanation of these phenomena depends on the meaning to be assigned to the 
remarkable modification of the electrical state of the leaf produced by moderate currents. 
On this point we can only express ourselves negatively. It is not analogous to an exci¬ 
tatory effect, for it is not capable of propagation : it is not identical with the after effect 
for it is transitory : it is not a polarization effect, for its direction is always the same as 
that of the cross difference whatever the-direction of the current which produces it. 
This fact also makes it impossible to identify it with Kunkel’s currents. The 
utmost that can be stated with reference to it is, that it indicates the occurrence of a 
