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]
DECOMPOSITION OF WATER.
To illustrate the decomposition of water, connect the copper strips, H
H, to the poles of the battery by means of wires, as shown in Fig. 3,
and insert them in a tumbler of water acidulated with a few drops of
sulphuric acid.
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