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. Instantly bubbles will rise from the copper strips,
showing that gas is being disengaged from the water. The strip
connected with the carbon plate will disengage oxygen, while the strip
connected with the zinc plate will disengage hydrogen.

[Illustration: FIG. 3.--DECOMPOSITION OF WATER.]


SOLENOID.