Ducretet Gold-Leaf Electroscope (ca. 1880s) |
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Gold leaf electroscope (ca. 10" high) for qualitative demonstrations of electrostatic phenomena. This design is essentially the same as the first gold leaf electroscope built by Abraham Bennet in the 1700s, and for this reason it is sometimes referred to as a Bennet-type electroscope. The body is glass while the circular base, the spherical contact and the lead-in are brass. The two gold leaves are both present although one is about half the length of the other. The result is that the shorter of the two leaves is deflected to a much greater extent than the longer one when the electroscope is charged. It might well have been this type of observation that led to the design of the single leaf electroscopes that substitute a fixed vertical rod for one of the leaves. The gold colored coating on the top portion of the glass is lacquer. If it had a purpose, that purpose is not known. It might just be that it got on the glass when a protective layer of lacquer was applied to the brass. Manufactured by the E. Ducretet of Paris, the famous French manufacturer of scientific instruments.
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Two metal rods ending in spherical knobs extend half way up the electroscope from the base. While their function is not perfectly clear, they may have served the same role as the two earthing strips that are often encountered in gold leaf electroscopes, i.e., to protect the gold leaves from the static charges that can accumulate on the glass. Another explanation was offered by Adolphe Ganot, author of what was probably the most widely used physics textbook of the nineteenth century: "the delicacy of this electroscope may be increased by adapting to the foot of the apparatus two metal rods, terminating in knobs; for these knobs, being excited by induction from the gold leaves, react upon them." |
