378 Rotary Multiplier, or Astatic Galvanometer. 
corresponding studs directly opposite. ps, ns, are stiff springs of 
copper, with silver tips at s pressing firmly against the studs on the 
cylinder, and connected with the mercury cups below. The back 
side of the instrument exactly corresponds to that exhibited in the 
drawing. ‘The modus operandi is seen at a glance. The two 
springs pn are connected by the mercury cups with the poles of a 
battery. The corresponding springs of the other side, with the 
wires of an electro-magnet for instance. By turning the cylinder 
half round, it is obvious the battery current is crossed, and the poles 
of the magnet reversed. 
New form of interruptor or electrotome.—As it is desirable that 
every distinct form of apparatus of general use should have an ap- 
propriate name, I have selected the term electrotome (divider of 
the electrical current) as applicable to the several varieties of appa- 
ratus figured and described in the July No. (1837) of your Journal. 
It is hardly necessary to premise, that secondary currents of great 
intensity, are obtained from a single pair of plates in connexion with 
the dynamic multiplier, when the primitive current is divided in any 
part of its course. - The force of the secondary current so obtained, 
depends materially upon the mode of breaking the circuit of the 
primitive. The shocks and decompositions I have found to be 
greatest when the primitive circuit is broken by raising clean pen- 
cils of lead, zinc or copper, from the surface of mercury covered 
