1854.] O¥ THE ROYAL INSTITUTION. 353 
absence of lateral induction) almost instantly attained. Then of 
course they discharge alike and therefore conduct alike. 
A striking proof of the variation of the conduction of a wire by 
variation of its lateral static induction, is given in the experiment 
proposed 16 years ago (1333.) If, using a constant charged jar, 
the interval s, page 6, be adjusted so that the spark shall freely 
pass there (though it would not if a little wider), whilst the short 
connecting wires 2 and o are insulated in the air, the experiment 
may be repeated twenty times without a single failure; but if 
after that, 2 and o be connected with the inside and outside of an 
insulated Leyden jar, as described, the spark will never pass across 
s, but all the charge will go round the whole of the long wire. 
Why is this? The quantity of electricity is the same, the wire is 
the same, its resistance is the same, and that of the air remains 
unaltered ; but because the intensity is lowered, through the lateral 
induction momentarily allowed, it is never enough to strike across 
the air at s; and it is finally altogether occupied in the wire, which 
in a little longer time than before, effects the whole discharge. 
M. Fizeau has applied the same expedient to the primary voltaic 
currents of Ruhmkorff’s beautiful inducting apparatus, with great 
advantage. He thereby reduces the intensity of these currents at 
the moment when it would be very disadvantageous, and gives us 
a striking instance of the advantage of viewing static and dynamic 
phenomena as the result of the same laws. 
Mr. Clarke arranged a Bains’ printing telegraph with. three pens 
so that it gave beautiful illustrations and records of facts like those 
stated : the pensare iron wires, under which a band of paper imbued 
with ferro-prussiate of potassa passes at a regular rate by clock-work ; 
and thus regular lines of prussian blue are produced whenever a 
current is transmitted, and the time of the current is recorded. In 
the case to be described, the three lines were side by side, and about 
0.1 of an inch apart. The pen m belonged to a circuit of only a few 
feet of wire, and a separate battery ; it told whenever the contact key 
was put down by the finger; the pen 2 was at the earth end of 
the long air wire, and the pen o at the earth end of the long 
subterraneous wire ; and by arrangement, the key could be made to 
throw the electricity of the chief battery into either of these wires, 
simultaneously with the passage of the short circuit current through 
pen m. When pens m and z were in action, the m record was a 
regular line of equal thickness, shewing by its length the actual time 
during which the electricity flowed into the wires; and the z record 
was an equally regular line, parallel to, and of equal length with the 
former, but the least degree behind it ; thus indicating that the long 
air wire conveyed its electric current almost instantaneously to the 
further end. But when pens m and 0 were in action, the o line did 
not begin until some time after the m line, and it continued after the 
m line had ceased i. e. after the o battery was cut off. Furthermore, it 
was faint at first, grew up to a maximum of intensity, continued at 
