424 TRANSACTIONS OF SECTION A. 
lead one to predict, with a high barometer and §.E. wind; near the ground they 
are more frequent in winter and at night. . ae 
The paper included in detail tables and diagrams illustrating and verifying 
the conclusions given, and a shorter discussion of several minor considerations. 
WEDNESDAY, SEPTEMBER 11. 
The following Papers and Reports were read :— 
1. The Current-Potential Curves of the Oscillating Spark. 
By 8. R. Miner, D.Sc. 
Two induction-coils connected in series were actuated by the same mercury 
break; one of these charged a Leyden jar battery and produced the spark, the 
other simultaneously discharged through a vacuum tube giving cathode rays 
which served as an indicator of the curves. The rays were deviated in two 
directions at right angles by the magnetic field of the spark current, and by the 
electric field of the spark p.d., and photographs of the resulting curves due to 
single sparks were presented to the Section. The oscillating discharge possesses 
a p.d. (35 volts) characteristic of the arc during the main part of each oscilla- 
tion, but a glow discharge with a p.d. of about 300 volts occurs for a short 
period when the current is changing sign. The curves confirm and extend 
Roschansky’s observations on the spark. 
A distinguishing feature of the oscillating spark is probably the comparatively 
low temperature of the instantaneous anode which exists in it. This view 
explains not only the occurrence of the glow discharge at the instant when the 
current is changing sign, but also the fact that the metal vapour streamers which 
are seen when the image of the spark is examined in a rotating mirror are 
invariably associated with the instantaneous cathode. The low temperature of 
the anode was ascribed to the effect of the different penetrating powers of the 
corpuscles and the positive ions which bombard the anode and the cathode 
respectively. The positive ions have a small penetrating power and expend 
their energy in raising the temperature of a layer of the cathode surface only a 
few molecules thick; the corpuscles with their larger penetrating power penetrate 
the anode to a greater extent, and consequently produce a smaller rise of 
temperature of the surface layer. 
2. A Case of Anomalous Conduction in a Solid Dielectric. 
By W. F. G. Swann, D.Sc. 
The conductivity of paraffin wax was investigated for potential gradients of 
the order of 100,000 volts per centimetre by a new method, and was found to 
increase with the field. 
A plate C was fixed between, and parallel to, two outer plates A and B, 
which were provided with guard rings. C was placed nearer to A than to B. 
The space between the plates was filled with paraffin wax, C being completely 
immersed in the wax. A and B being earthed, C was charged through a fine 
hole in the wax, the hole being afterwards sealed up. The plates A and B were 
released from earth at intervals, and their rates of alteration of potential were 
noted. By plotting this quantity against the time, two curves were obtained, | 
one for A and the other for B. The corresponding ordinates for the two curves 
were found to be equal but of opposite sign. Theory shows that if Ohm’s law 
is obeyed neither A nor B should alter in potential as the electricity leaves C, 
the rise of potential of A, for example, due to the passage of electricity from C 
to A, being just counterbalanced by the fall due to the transference of elec- 
tricity from C to B. If the conductivity decreases with the field we should find 
that if C is positively charged, B rises and A falls. If the conductivity increases 
with the field we should find, as was actually found, that A rises and B falls 
in potential. The paper concluded with a discussion of the theory of dielectric 
conduction, 
