G. F. Barker—New Vertical-lantern Galvanometer. 211 
is evidently capable of producing a galvanometer for demon- 
stration, whose delicacy may be determined at will, depending 
only on the kind of work to be done with it. In the first 
place, the needles may be made more or less perfectly astatic 
and so freed more or less completely from the action of the 
earth’s magnetism, and consequently more or less sensitive. 
Moreover, an astatic system seems to be preferable to one in 
experiments, the considerable distance which separates the nee- 
dles in this instrument, allows the use of a damping magnet 
with either of them. In the galvanometer now in use, the 
upper needle is the stronger, and gives sufficient directive ten- 
dency to the system, to bring the deflected needle back to zero 
quite promptly. In the experiments referred to below, the sys- 
tem made 265 oscillations per minute. 
Secondly, the space beneath the mirror is sufficiently large 
to permit the use of a coil of any needed size. Since, there- 
fore, the lower needle is entirely enclosed within the coil, the 
field of force within which it moves, may be made sensibly 
equal at all angles of deflection, as in the galvanometers of Sir 
William Thomson. Hence the indication of the instrument 
may be made quantitative, at least within certain limits. The 
circular coil too, has decided advantages over the flat coil, since 
the mass of wire being nearer to the needle, produces a more 
astatic combination, could be placed below the mirror, the up- 
per needle in that case serving only as an index. The instro- 
ment above described has a coil three inches in diameter and 
one inch thick ; the diameter of the core being one inch. Since 
\ts resistance is only about a quarter of an ohm, it is intended 
for use with circuits of small resistance, such as thermo-currents 
and the like. 
The results of a few experiments made with this new vertical- 
lantern galvanometer will illustrate the working of the instru- 
ment and will demonstrate its delicacy. The apparatus used 
was not constructed especially for the purpose, but was a part 
of the University collection. : 
Anduction Ourrents.—1. The galyanometer was connected 
With a coil of covered copper wire, No. 11 of the American 
Wire gauge, about ten centimeters long and six in diameter, hav- 
Ing a resistance of 0-323 ohm. A small bar magnet 5 centimeters 
long and weighing six and a half grams, gave, when introduced 
into the coil, a deflection of 40°. On withdrawing the magnet, 
the needle moved 40° in the opposite direction. 
2. A small coil, 20 centimeters long and 3% in diameter, 
made of No. 16 wire and having a resistance of 0371 ohm, 
