174 M. W. Siemens on the Admissibility of the 
If the similar electricity accumulated in the part of the 
conductor most distant from the sphere finds a means of 
transmission to still more distant conductors, the first con- 
ductor becomes lastingly charged with electricity the polarity 
of which is the opposite of that of the sphere. But if the 
elevation of the conductor above the surface is but little in 
proportion to the diameter of the sphere, then the difference 
of tension between the surface of the sphere and the most 
distant point of the elevation can only be small. For this 
reason, even with a great density of the electricity on the 
surface of the earth no electrical repulsion can take place 
there, and even on mountain-tops it cannot be very noticeable. 
But the ratio takes another form when a sphere is charged by 
induction from a distant electrical sphere. The lines of force 
which, according to Faraday's molecular-distribution theory, 
go from the charging to the charged sphere from which the 
electricity is carried away, meet the latter everywhere almost 
perpendicularly and, with a great distance between the in- 
fluencing spheres acting upon each other in proportion to 
the diameters of the spheres, in almost equal number on 
the side turned towards the distributing sphere and on that 
turned away from it. If now an insulated conductive screen 
that covers a part of the surface of the influenced sphere be 
brought near the latter, if it be thin it will not become 
perceptibly electric. But as soon as the screen is touched so 
as to conduct away its electricity, it takes the opposite elec- 
tricity to that of the sphere, while the like electricity is 
carried away. The behaviour is the reverse of this when the 
screen is conductively connected with the sphere ; the screen 
then forms part of the surface of the sphere and receives its 
electric charge, while the part of the surface under the screen 
becomes nonelectric. Now the thunder-clouds appear in the 
character of such screens upon the surface of the earth. If such 
a screen of cloud be imagined included in the formation over 
a part of the earth's surface, it will remain unaffected by the 
earth's electricity so long as the conductive particles of water 
are insulated and at a considerable distance from one another. 
Hence mist and light clouds will not become electric. But as 
soon as the mist has so far condensed that its conductive parts 
come into contact with one another, or the distance between 
them becomes so small that electricity of very slight tension 
can overleap the intervals, the cloud is subjected to the distri- 
bution process. This can be initiated by its being put into 
conducting connexion with clouds situated in very elevated 
regions by ascending cloud vortices. This conductively con- 
nected cloud is then electrified in its lower part with the 
