312 Intelligence and Miscellaneous Articles. 
coil consists of a total length of 1660 feet of No. 22 copper wire, 
weighing rather more than 6 lbs., and divided into four parts, the 
ends of which are brought out and connected with their respective 
terminals G G, so that they can be used separately or as one coil. 
The needle with which the first experiments were made consisted of 
a small rectangular steel bar, 14 inch in length, rather less than jth 
of an inch in breadth, and about half the thickness of a shilling. It 
weighed exactly 18 grains, and, when magnetized, its lifting power 
was 44 grains, or nearly 24 times its own weight. The index M, 
which is 9 inches in length, weighs only 2 grains. A small brass 
pulley, 4th of an inch in diameter, is fixed upon the axis between the 
index and the supporting screw L. ‘The balanced lever E H consists 
of a thin shp of hard spring-brass, placed edgewise for strength, and 
tapered, for lightness, towards the end of the long arm AH. The 
short arm A E is loaded to act as a counterpoise; and to this arma 
scale-pan C is suspended, at a distance from the fulcrum equal to 
exactly 5th of the length of the other arm. It carries also at its 
extremity a thin horizontal projection, which vibrates between two 
screw-points D, D’, and by which, with the aid of the wooden foot- 
screws of the instrument, the lever can be always Fig. 2. 
exactly levelled when balanced. ‘The fulcrum 
B is supported on a stout brass bar F, which is 
firmly held in its place by means of the screw I, 
and can be removed at pleasure. When it is 
desired that the needle shall have hberty to 
move in both directions, the extremity H of the 
long arm of the lever is connected with the 
needle by a slender wire suspended from a very 
fine thread, fixed to the upper part of the pulley 
and carried down on both sides of it, as shown 
in fig. 2. The arm AH is divided into ten 
equal parts, each of which is subdivided into 
tenths ; and, estimating the poles of the needle 
to be at a distance of about 4th of its total length 
from the extremities, the diameter of the pulley 
is so adjusted that a weight of 100 grains, sus- 
pended at the distance of one of the large divi- 
sions from the fulcrum, acts with a force of 1 
grain at the poles of the needle; suspended at 
division 2, it acts with a force of 2 grains; at 
2°5, with a force of 21 grains, and so on. 
‘The following Table exhibits the results of the first series of expe- 
riments made with a small Grove’s battery, the platinum plates of 
which expose only two inches of surface, and having the zine plates 
immersed in a saturated solution of chloride of sodium. It is a 
striking characteristic of Grove’s battery that it slightly increases in 
force after being some time in action; and it would have been pre- 
ferable, therefore, to use a Daniell’s, on account of its remarkable 
constancy ; but the writer had not a sufficient number in series. The 
fourth column indicates the weight required to bring the index of 
