92 Prof. Faraday on Electric Induction— 
ment proposed sixteen years ago (1333). If, using a constant 
charged jar, the interval s, page 90, be adjusted so that the spark 
shall freely pass there (though it would not if a little wider), 
whilst the short connecting wires m 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 elec 
tricity is the same, the wire is the same, its resistance is the 
same, and that of the air remains unaltered; but because the in- 
tensity is lowered, through the lateral induction momentarily al- 
lowed, it is never enough to strike across the air at s; and it!s 
finally altogether occupied in the wire, which in a little longer 
time than before effects the whole discharge. M. Fizeau has ap- 
plied the same expedient to the primary voltaic currents of Ruhm- 
korff’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 very stir 
king instance of the advantage of viewing static and dynamic 
phenomena as the result of the same laws. 
Mr. Clarke arranged a Bain’s printing telegraph with three 
pens, so that it gave beautiful illustrations and records of facts 
like those stated; the pens are iron wires, under which a band 
of paper imbued with ferro-prussiate of potassa passes at a regu 
lar 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 pet 
nW 
sline of equal thickness, showing by its length the actual time 
during which the electricity flowed into the wires; and the” 
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 instal 
taneously to the further end. But when peus m and o were 0 
action, the o line did not begin until some time after the m lin® 
and it continued after the m line had ceased, 7. e. after the 0 bat 
tery was cut off. Furthermore,: it was faint at first, grew up '° 
a maximum of intensity, continued at that as long as battery co™ 
= ae 
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