Chatlock's Gold-Leaf Electroscope by Griffin (early 1900s)

 

This is an early condensing electroscope that was intended for qualitative demonstrations of electrostatic phenomena. The single leaf, still attached at the bottom of the support (conductor) rod, is aluminum. A three inch diameter brass condenser (Volta) plate is connected to the top of the rod. The front and back of the case are glass. The top, bottom and the two sides are sheet metal.  

The defining characteristic of this instrument is the long ribbed insulator (probably ebonite) that surrounds the support rod and separates the latter from the metal case. A nice explanation for how the insulator minimizes electrical leakage between the case and the rod-leaf-condenser is provide by Hadley (1913):

"Nearly all the leakage which may occur is conveyed along the surface of the insulating plug; the insulation is therefore improved by cutting V-shaped grooves on the surface of the plug, whereby the length of path traversed by any leakage is increased."

This tells us that the electroscope in the photo needs an adjustment. The distance from the top of the case to the top of the insulator should be the same as the distance to the bottom of the insulator. Just like the drawing.

 

In general, an electrophorus would be used to transfer a charge to the condenser.  For an explanation of how an electroscope can be charged and how an electrophorus works, click here. 

The maker's name is stamped on the top of the metal case: GRIFFIN, LONDON. A small plate on the inside the case, located just below the support rod, reads: Gramme Standard.  Since it is my understanding that Griffin changed their name to Griffin & Tatlock sometime between 1910 and the late1920s, it seems reasonable to date this instrument from 1900 - 1920.

The figure below, taken from an undated Max Kohl catalog, shows a similar instrument. The catalog description reads:

"Electroscope, Chatlock's. Figure, with first-rate ebonite and air insulation, with aluminum leaf, also suitable for projection."

300

The same type of instrument is described as a gold leaf electroscope in a 1908 catalog published by Philip Harris & Co. Their detailed description follows:

"Comprising two narrow strips of gold leaf suspended from the lower end of a brass rod, at the top of which a metal disc is fixed. The wire [rod] is supported vertically by a a plug of insulating material (ebonite), and the leaves are protected from air currents by means of a case, the front and back of which are glass. The sides of the case are lined on the inside with strips of metal, which are earth connected. The insulating plug has V-shaped grooves on the surface to increase the length of the path of the leakage, which is conveyed along the surface of the insulating plug."

 

This is identified as "Chatlock's electroscope" because that is the name given to it in the Max Kohl catalogs. However, I have never seen this name employed anywhere else. Perhaps the design was associated in some way with A. P. Chatlock, a physics professor at University College (Bristol) in the late 1800s.

Size: ca 8" tall. The chamber is 5" high, 4" wide and 4" deep. The condenser (Volta) plate is ca. 3" in diameter. The wooden base is 5" x 8".

References

Hadley, H.E. Magnetism and Electricity for Students. 1913.

Max Kohl A.G. Chemnitz. Physical Apparatus. Price List No. 50. Vols. II and III. No date.

Philip Harris & Co. Ltd. Explanatory Price List for Physical Instruments. 1908.

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Last updated: 07/25/07
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