104 Notice of a Galvanometer. - 
steel wire and is partly neutralized by being connected with a second 
and more delicate needle, made of the smallest species of main 
spring. This second needle is parallel to the principal one, three 
eights of an inch above it, and with its poles reversed in the manner 
of M. Nobili. It is intended to act chiefly as an 1npEx and swings 
above the card. The two needles are firmly connected together by 
abrass wire. ‘The whole is closed by a glass cover in the manner of 
a common compass, which it nearly resembles in external appearance. 
The glass is however pierced in its center by a hole half an inch in di- 
ameter, for the insertion of a perpendicular brass tube, four inches 
high. ‘This tube includes the suspension filament which is fastened 
to the center of the cap the latter being closed at the top. The pro- 
jecting wires ascending in an arch, and approaching within a quarter 
of an inch, terminate, the one in a five cent piece of silver, and the 
other in a corresponding disc of zinc. Three projecting brass feet, 
with each a levelling screw, support the instrument. 
A wine glass of water, applied once to the discs, will deflect the nee- 
dle from two to five degrees; by repeated applications the needle 
may be made to vibrate through sixty degrees. When the conjunc- 
tive wires of a calorimotor of one and half square feet of zinc, 
filled with rain water, are laid on the poles of this galvanometer, the 
needle is deflected to ninety degrees which is the maximum. If it 
be suffered to remain thus in action, it will retain the needle at about 
seventy degrees for twenty four hours; how much longer I have not 
yet determined. 
The advantages which it seems to me, my instrument possesses 
are, that the ‘‘ multiplying” coil being brought the nearest possible 
to the needle must affect it the most sensibly ; being entirely enclosed, 
it is not disturbed by the agitation of the air; it is compact and 
elegant in its form. 
Fig. 1. Is a plan of the ring R, and coil of wire W, half size. 
Fig. 2. Is a section of the whole instrument. B.'The box. R. 
The ring. W. The wire. N.S. The needle. n.s. The index. 
D. The dial cut out in the center to show the wires and to permit 
the needle to be introduced or withdrawn readily, through the open- 
ing O. C. The wire connecting the index and needle. G. The 
glass cover. ‘I’. The brass tube including the suspension filament F’. 
Fig. 3. The perspective view, in which the corresponding parts 
are marked with the same letters as in fig. 2. P. Is an ivory pin 
