In making electrical diagrams it is necessary to frequently represent
a battery. It requires too much time to make a sketch or drawing of a
battery. Besides this, the drawing of any particular kind of battery
might be misleading. A sign representing the galvanic battery has been
universally adopted. It consists of a long, thin mark or dash,
representing the carbon electrode, and a shorter, thick mark
representing the zinc electrode, thus: [Illustration] Where more cells
are required, this sign is repeated once for each cell, thus:
[Illustration] The galvanometer is represented thus: [Illustration]
By the use of the battery and a few articles such as may be found
anywhere, in addition to the pieces shown in Fig. 2, all the
experiments here described may be performed. As these pieces are shown
half size in the diagrams, Fig. 2, and about full size in the
perspective views, it will be unnecessary to give dimensions. The
bobbins, A A, are wound with No. 24 double cotton-covered magnet wire,
the terminals being soldered to eyes formed of pieces of spring wire
bent so as to form helical coils of two turns each, with the ends
inserted in holes drilled in heads of the spools. These coiled wires
answer a good purpose in making electrical connections. The magnet
frame, B, consisting of the cores and the yoke formed integrally of a
single soft gray iron casting, is adapted to receive the bobbins, A A,
to form an electro-magnet. The yoke of the magnet is provided with a
thumb-screw, e, for securing the magnet to the motor frame, C. The
latter is furnished with a base piece, f, a slotted standard for
receiving the clamping screw, e, of the magnet, and the standards, g,
in which is journaled the armature, h, on a wire extending through
both the standards and the armature.
The armature, h, consists of an oblong rectangular soft iron frame
having at one end a small pulley and at the other end an elliptical
boss, i, which is arranged obliquely to form in conjunction with the
spring, j, a circuit closer and opener, which closes the circuit twice
during each revolution of the armature, just as one of its side bars
is approaching the poles of the magnet and breaks it as the bar comes
opposite the poles of the magnet.
The spring, j, is bent into a loop and its lower end is inserted in a
wooden plug driven into a hole in the base piece, f.
In the upper part of Fig. 2 are shown two telegraph instruments less
the bobbins. Each instrument (Fig. 14) consists of a wooden base, k, a
right angled soft iron bar, l, having the central part of its upper
end brought to an obtuse angle, an armature, m, fitted loosely to the
angled end of the bar, a notched brass standard, n, for limiting the
movement of the armature, a retractile spring for lifting the
armature, a spring key, o, pivotally secured to the base by a common
wood screw, and a contact point projecting from the base under the
key.
Besides these there is a D shaped block, to answer as a frame to the
galvanometer, a common pocket compass, E, fitted to a circular cavity
in the top of the block, D, a permanent U magnet, F, a bundle of soft
iron wires, G, and two copper strips, H.
[Illustration]