Scientific American Supplement, No. 794, March 21, 1891

Excerpt

ELECTRICAL LABORATORY FOR BEGINNERS.

By GEO. M. HOPKINS.

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.

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....