bn, 
2A2 sat Arial Galvanometer. 
Arr. XI.—Azial Galvanometer ; by Cuartes G. Pace, M. D., 
Prof. Chem. and m., Columb. Coll., Washington, D.C. 
Tur Galvanometer or Galvanoscope, as usually constructed, I 
have before stated is far from being a reliable instrument, for sev- 
eral distinct reasons. First, if the needle is not of the hardest 
steel, its power is constantly varying, under the influence of vary- 
ing currents in the coil of wires. The magnetic force of the nee- 
dle tends constantly to diminish, and the action of a powerful cur- 
rent is to give it an extra charge, and should its position be acci- 
dentally reversed, that is, be the reverse of that which it would 
assume under the action of the current, its polarity will be revers- 
ed, or its foree much weakened. Any variation in the force of 
the needle during the course of investigation, must necessarily be 
productive of error in the results. Again, it is exceedingly diffi- 
cult to render a needle perfectly astatic, or to divest it of local in- 
_ fluences when the single needle is used. Again, in operating 
with high galvanic powers, the differences of deflection are almost 
imperceptible, and the estimates become exceedingly complicated. 
By substituting for the magnetized needle, a wire of soft iron, we 
gain in several particulars. First, the wire has no magnetic pow- 
er, above that which is due to the retentive power of the soft iron, 
which may be considered as nearly a constant quantity. Second, 
the deflective force is not called into action, and therefore the ob- 
servations are not complicated by fluctuations in the earth’s action, 
or local forces. In using the galvanometer ordinarily, the degree 
of deflection is the difference between the earth’s action, or the 
compound ratio of the earth’s action and a local magnet, and the 
action of the galvanic current, or else the difference between the 
deflective force of the current upon an anastatic needle and the 
force of torsion. The axial galvanometer is sufficiently sensitive 
for most persons, is more delicate than I had anticipated, and it” 
has the advantage of being rendered more or less sensitive at pleas- 
ure. In Vol. xx1x, p. 137, of the former series of this Journal, I 
gave an account of an axial galvanometer, in which it was neces- 
sary to use the spring balance to determine by weight the amount 
of forces. In the instrument now presented this difficulty is ob- 
viated, and the iron wire within the coil constitutes the balance 
itself. In the first form, the use of the spring or lever balance 
