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Dry-Pile Electroscope
England, Watkins & Hill, 1822-1856
If there were a strong electrical field, even a weak charge on the gold foil would cause it to move. A dry Voltaic Pile can do the job. A regular Voltaic Pile is an electrochemical battery, with alternating silver-zinc-cloth, silver-zinc-cloth, silver-zinc-cloth stacked one on top of another. Then, when it is soaked in a weak acid, the cloth becomes wet and the Pile produces a fairly high voltage. A dry pile is not truly dry - it uses atmospheric moisture to promote its electrochemical action. At the same time, "soaked" is not an appropriate word, and the dry pile will certainly not drip like a regular Voltaic Pile. Since the electrochemical action is weak, the metals in the pile do not corrode noticeably. They can be thin foils; and the cloth can be replaced by paper. You can build a dry pile with thousands of layers that is still a reasonable size, and it will produce thousands of volts at a very tiny current. This voltage can provide the constant electric field needed for the electroscope. As a bonus, with a static electric field, this electrometer can tell you the polarity of your charge - positive or negative. To make this particular electroscope even more sensitive, it is arranged as a condensing electroscope. (The upper, removable, half of the condenser has been lost.) In operation, there would be a single strip of gold leaf hanging down from the brass rod inside the jar. It would be in the electric field of the two brass balls on top of the two dry piles, and would move left or right with the applied charge. Some of these dry-pile electroscopes included calibrated scales to measure charge (or voltage) more precisely. |
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If you put a charged object into an existing electric
field, it will move. A regular