BEFORE AND AFTER COMPLETION OF THE VOLTAIC CIRCUIT. 
43 
16. When the micrometer electrometer, described in my former paper* was intro- 
duced between the terminal wires, sparks, through the space of -g^th of an inch, were 
obtained ; and when the double electroscope (fig. 4) was included in the circuit, and 
the discs a and b were approximated, an uninterrupted succession of sparks would 
pass between the discs. These effects, which I have repeatedly shown to many 
friends, are most brilliant. On one occasion they were continued uninterruptedly 
day and night for upwards of five weeks; and although some months have now 
elapsed since this battery was completed, it still exhibits the same effects. 
1 7. When the experimenter was standing on the ground, and consequently, as has 
been already explained, in actual, although imperfect connection, with the battery, he 
could draw sparks from either terminal. We shall, in the sequel, be enabled to trace, 
with more precision, the rise of this tension ; for the present, we are only concerned 
in establishing its existence, and thereby proving the first fact, that tension or electro- 
static effects precede, and are independent of, the completion of the voltaic circuit. 
18. Hitherto we have not obtained any insight into the condition of the dynamic 
effects under such circumstances of antecedent tension. For testing the presence 
of what is usually termed the current, or in other words, obtaining the means of 
observing the electro-dynamic effects, I used the instrument which is best suited 
for examining such phenomena, and which invariably attests the instant completion 
of a voltaic circuit. An exceedingly delicate galvanometer was introduced at B (see 
fig. 1), and the two condensing plates a and b of the double electroscope (fig. 4) were 
respectively attached by wires to the terminals N and P of the battery, fig. 1. If 
great care was taken not to make any connection with the ground, the party mani- 
pulating being himself well insulated on shell-lac, no action could be perceived on 
the needle in the galvanometer, although the gold leaves of the electroscope imme- 
diately diverged to a very considerable extent. 
19. This experiment was, however, of too much importance to be passed over 
without adopting every means of making it unexceptionable. Two trays from the 
battery, being a series of 160 cells, were removed and insulated, by being supported 
on stout varnished glass pillars twelve inches high ; the whole being placed upon an 
Arnott’s stove in which a fire had been kept burning for several hours. The galva- 
nometer was interposed between the zinc terminal of one tray and the copper terminal 
of the other ; and the extremities of this reduced series were arranged so as to exhibit 
the same effects of electric tension which we have seen in the entire series ; but not 
the slightest indication of dynamic action could be detected by the galvanometer. 
The action of the instrument I used could not be in fault ; and some idea may be con- 
ceived of its extreme delicacy, when I state that, with one cell of the gas battery-f- I 
have obtained a steady deflection, whilst a resistance of twelve miles of thin copper 
wire was interposed in the circuit ; when the electroscope (fig. 6) was used, c c' being 
respectively connected with N and P of battery, the gold leaves b b', were attracted ; 
* Philosophical Transactions, 1840, p. 184, § 12. f Ibid. 1843. 
