It is only when theory and practice, study and experiment, go hand in
hand that any true progress is made in the sciences. A head full of
theory is of little value without practice, and although the student
may apply himself with all his energies for years, his time will, to a
great extent, have been spent in vain, unless he by experiment rivets
the ideas he gains by his study.
In the study of electricity, for example, let the student try to
remember the position a magnetic needle will take when placed below or
above a conductor carrying a current which flows in a known direction.
Without experiment there are nine chances of forgetting to one of
remembering; but let the student try the experiment, and he will ever
afterward be able to determine the direction in which the current is
flowing by the position taken by the needle relative to the conductor.
In the matter of ampere turns, as another example, it is quite simple
to assert that a ten ampere current carried once around a soft iron
bar produces the same result as a one ampere current carried ten times
around the bar, but how much more strongly is this fact stamped upon
the memory when its truth is established by experiment?
Reading about a fact, or commiting to memory the literature of a
subject, is desirable and even necessary, but knowledge of this
character partakes more of the nature of faith than that gained by
actual experience.
Let the reader learn first all that can be learned by the aid of this
simple apparatus, then branch out to allied things, making each step
as thorough as possible, and before long he will be congratulating
himself on having gained at least an elementary knowledge of
electricity.
Very little can be done in the way of electrical experiment without an
electrical generator of some sort, and nothing at present known can
excel a battery for this purpose. Although not the most desirable
battery for all purposes, that shown in Fig. 1 is the most desirable
for the amateur who desires a strong current for a short time. It is
formed of two plates, a, of carbon arranged on opposite sides of an
amalgamated plate, b, of zinc, and separated from the zinc by strips
of wood. Bars of wood are placed outside of the carbon plates, and the
four bars are fastened together by two common wood screws, thus
clamping all the bars and the zinc and carbon plates securely in the
position of use.
[Illustration: FIG. 1.--SIMPLE BATTERY.]
Between the zinc plate and the wooden bar adjoining it is inserted a
strip of copper, c, for leading away the current from the zinc pole of
the battery, and between the carbon plates and the wooden bars is
inserted a doubled strip of copper, d, forming a connection between
the two carbon plates, and at the same time serving as a conductor for
conveying away the current from the carbon pole of the battery. This
element is to be plunged into a tumbler of sufficient depth to allow
the wooden bars to rest on the upper edge of the tumbler, while the
lower ends of the plates are one-half or three-quarters inch above the
tumbler bottom.