— 
+ é 
On Ellectro-Dynamic Induction. 119 
per and zinc as usual are separated by a membrane, on both sides 
of which is placed a solution of one part of sulphuric acid in ten 
parts of water; and to this is added, on the side next the copper, 
as much sulphate of copper, as will saturate the solution. The 
battery was sometimes used as a single series, wit its ele- 
ments placed consecutively, and at others in two or series, 
arranged collaterally, so as to vary the quantity and sity of 
the electricity as the occasion might require. 
4, The galvanometers mentioned in this paper, and referred to 
in the last, are of two kinds; one, which is used with a helix, to 
indicate the action of an induced current of intensity, consists of 
about five hundred turns of fine copper wire, covered with cotton 
thread, and more effectually insulated by steeping the instrument 
in melted cement, which was drawn into the spaces between the 
spires by capillary attraction. The other galvanometer is formed 
of about forty turns of a shorter and thicker wire, and is always 
used to indicate an induced current, of considerable quantity, but 
of feeble intensity. The needle of both these instruments is 
Suspended by a single fibre of raw silk. 
5. [should also state, that in all cases where a Saisie 
spiral is mentioned in connection with a helix, the article is 
formed of a long, fine wire, making about one hundred turns 
around the axis of a hollow piece of straw, of about two inches 
and a half long: also the spiral mentioned in connection with a 
coil, is formed of a short wire, which makes about twenty turns 
around a similar pieee of straw. . The reason of the use of a 2 
two instruments in these two cases is the same as that for t 
galvanometers, under ilar circumstances, namely, the helix 
ensity, but of small quantity, met the coil 
gives a current of i 
SIT) 
whee = one of conside is -nacad but of fee 
, dsecrestiih is 1 oi aia 
On the Inti the ie Beginning of @ 
Galvanic | 
6 Ie wil bo'tosleets 
ployed in my last series o! 
at the moment ieiaking the galvanic circuit, 
d that the arrangement of apparatus em- 
f experiments gave a powerful induction 
t the effect at 
making the same was so feeble as rg 
se and tit 
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