Rotary Multiplier, or Astatic Galvanometer. 377 
and powerful, and the mode of suspending the wire allows it to be 
brought much nearer the magnet than is represented in the figure ; 
at the same time the friction is trivial The apparatus would be 
much improved by the addition of another bar magnet n’ s’ above 
the coil. In that case the magnetism of both bars might be pre- 
served, by arming their opposite poles when not in use. This in- 
strument, though interesting, is not intended as a measurer of gal- 
vanic force. But the principle of making the conducting wires the 
indicators instead of the magnets, appears to be of value, for many 
reasons. The conducting wires may be considered as perfectly as- 
tatic, and affording eonstant results. It is difficult to obtain, and 
much more so to preserve a perfectly astatic needle. The needle 
of a galvanometer is readily disturbed by the approach of any ferru- 
ginous body. By substituting for the dissected cylinder at a two 
entire cylinders above and below, the rotary multiplier becomes a 
galvanoscope of considerable delicacy. In order to constitute an 
astatic galvanometer the whole should be inverted, the magnets sup- 
ported from below, the multiplier by a torsion thread from above, 
and the extremities of the wire turn in small mercury cups in the 
centre of motion. 
Fig. 2, represents a new form of electrepeter. Its name purports 
a turner or changer of the electrical current. An ingenious appara- 
tus of this kind, by Mr. Clarke of London, is described and figured 
in the first No. of Sturgeon’s Annals ; but it is not so simple in con- 
struction, and the connecting wires in his machine being out of 
sight, it is not so easily understood as the one here figured. The 
drawing represents a double electrepeter, or one to be used with 
two separate batteries, and two or more pieces of electro-magnetic 
apparatus. Divide the machine at a, and bring up the wooden 
pillar r to the left hand division, and you have the single electre- 
peter, answering for most purposes. ‘The one | have constructed, 
was made for reversing the motion of an electro-magnetic engine, 
and has four parts. a c is a cylinder of mahogany 3 inch diameter, 
mounted for semi-rotation between two wooden pillars. b 606 
represent strips of silver passing each obliquely half round this cyl- 
inder, and fastened to it by pins of the same metal. 0’ 0’ b/ b’ repre- 
sent rectangular studs of silver, (copper will answer, but not so 
well,) connected metallically through the centre of the cylinder with 
* The wires here should be of silver, except the tips for the mercury connexion. 
