A popular sketch of electro-magnetism, or electro-dynamics / ... By Francis Watkins.

  • Watkins, Francis
Date:
1828
Catalogue details

Licence: Public Domain Mark

Credit: A popular sketch of electro-magnetism, or electro-dynamics / ... By Francis Watkins. Source: Wellcome Collection.

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    To this apparatus Dr. Wollaston recommended the important addition of surrounding the single plates of zinc with copper; the power of the zinc being obviously increased by extending the cop- per plate so as to oppose it to every surface of the zinc, contact of surfaces being prevented by small pieces of cork or wood. This apparatus is best adapted to all the researches in which there is a demand for quantity as well as intensity of electric fluid. For experiments in electro-magnetic science, a battery, similar in construction to the calorimotor of Professor Hare, is to be pre¬ ferred, as being the most (economical and affording greater facilities to the experimenter. It consists of two fixed hollow concentric cylinders of copper, having a moveable cylinder of zinc placed between them : one great advantage which this construction pos¬ sesses is, that after every experiment the zinc cylinder may be taken out, and the oxide which is formed on its surface removed; the battery being thus restored to its original state of activity. This contrivance, we believe, is due to Mr. Sturgeon of Woolwich, and it will be seen how admirably it is adaptecf for the purposes to which he has applied it. A number of batteries may be joined together by merely ar¬ ranging a metallic communication between the copper extremity of one battery and the zinc extremity of the other. By this me¬ thod of multiplying the number of plates we obtain electricity of a high intensity, and the proportion is as nearly as can be judged an arithmetical one. By enlarging the size without increasing the number of alternations, we gain not in intensity, which remains exactly the same, but in quantity. The term quantity is employed to express the real quantity of electric power in a body, and zVi- tensity or tension its power of transmission through imperfect con¬ ductors. The relative effects of quantity and intensity were admirably il¬ lustrated by the experiments instituted by Mr. Children, whose vol¬ taic combination consisted of plates thirty-two inches wide and six feet high. The effect upon perfect conductors was intense, but upon imperfect conductors feeble. Different degrees of chemical action are produced on the metallic plates by the various fluids used to excite the voltaic apparatus; and the more powerful the action produced, the more transient is its duration. To obtain an apparatus which would continue in force during
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