London Electrical Society. 491 
These positions were supported by several new experiments with the 
double electroscope. The author then explains an imperfect state 
of charge consequent on the discharge of a system which developes 
on the outer coating a certain quantity of free electricity, to which 
Mr. Walker gives the name ‘induced residual.” He assumes a 
case of 100 Harris’s units being thrown on one coating of a jar 
while 90 are expelled from the other, on the well-known principle 
that one coating always possesses an excess over the other; the 
outer coating in this case has a capacity and attraction for 90. If, 
however, the discharge is made and 90 pass, the whole of the 90 
cannot abide there, because the 10 remaining in the jar would re- 
quire a dispersion of 9 from the outer coating. This 9 is termed the 
“« induced residual,’”’ and is shown to bear direct ratio to the excess 
and the flash. If represent the ratio of excess and @ the flash, 
the induced residual « is equal to @ —- < .¢. But in the case 
of clouds both n and ¢ are very great, and therefore the free elec- 
tricity x is at a maximum. The author then shows experimental 
illustrations of lateral sparks, and traces their dependence on this 
induced residual ; from which he draws the inference of similar phe- 
nomena occurring on an immensely larger scale in the discharge of 
lightning, and illustrates his inference by the phenomena observed by 
Mr. Weekes with his atmospheric apparatus, and also by experiments 
with the prime conductor, which he shows to be not so dissimilar to 
a charged cloud as some have imagined. He now traces the action 
of the part of the flash actually required to compensate the excited 
; rat! ? 
area of the earth; its value is oe @; it enters the earth at one spot, 
and is required for compensating a Jarge area. The comparatively 
low conducting power of the earth greatly resists its diffusion, and 
induces a tendency to divide into several paths; and possibly some 
portion even of this may be converted into free electricity, from the 
fact that the compensation of the extreme verge of the disc could be 
more readily effected by the return of the electricity from the adja- 
cent lower stratum than by the diffusion of the flash from the one 
centre. Mr. Walker then reports several instances of accidents 
having occurred from the division of lightning-flashes from the con- 
ducting rod over other adjacent bodies, even when the rod was of 
standard size, and perfect in all its parts. From all which he infers 
that it is a matter of vital importance to connect such bodies with 
the rod, an inference which he confirms by a mass of testimony from 
the best sources. In the course of the memoir a modification of the 
dise experiment is introduced, in which the vicinal body is between 
the discs, but connected with the earth by means of a wire passing 
through a glass tube in the lower disc. Sparks occur in this case as 
they did in the experiment of erecting rods on the floor of the room. 
Mr. Walker then shows how a copper-bottomed vessel protected by 
Mr. Harris’s conductor resembles the lower disc, and, from the fact 
of no spark passing when the vicinal metal touches the lower disc, 
he infers, @ fortiori, that no spark can leave one of Mr. Harris’s rods 
