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declination, the reference to the meridian is not required. 
Here, therefore, the theodolite and transit instrument are un- 
necessary, and the former will be replaced by a fixed teles- 
cope, furnished with a finely divided micrometer scale in its 
focus. 
A similar apparatus serves for the determination of the 
changes in the horizontal magnetic force. It is only neces- 
sary to modify a little the suspension arrangement, and to 
substitute for the single thread two equidistant threads ; as 
in the torsion electrometer of Mr. Snow Harris. The needle 
is then to be turned by the force of torsion, into a position 
at right angles to the magnetic meridian; in which position 
the momentum of the magnetic force is greatest. The 
changes of position of the bar (read off as before by a fixed 
telescope with a micrometer scale) will enable the observer 
to deduce, by an easy formula, the corresponding changes of 
the magnetic force. Professor Lloyd then entered into some 
details connected with the theory of the instrument as thus 
employed; and he showed in what manner it was to be ad- 
justed, so that a given variation of the magnetic force might 
produce the greatest variation in the position of the bar. 
A paper was read by Edward S. Clarke, Esq., on an Im- 
provement which he had lately made in the Sustaining Bat- 
tery, and on the size proper to be given to the zinc element of 
sustaining batteries in general. 
The author alluded to the decline of voltaic power which 
occurs during experiment, and ascribed to M. Becquerel the 
credit of having assigned its true cause; referring it, as this 
philosopher did, to a transfer of the decomposed substances 
to the respective plates, in such a way as to produce secon- 
dary currents moving in a direction reverse to the primary 
current. 
Mr. Clarke also alluded to the fact, that Becquerel was 
the first person who, to remedy this evil, adopted, in 1829, 
