204 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



in which the gold leaves are insulated. The cap is a flat 

 plate with a wire soldered beneath. The gold leaves are 

 soldered at the lower end of the wire, and the whole wire 

 is inclosed in a giass tube. The outer surface of this tube 

 is best covered with sealing-wax, as the insulation of resinous 

 substances is much better in damp weather than that of 

 glass, which rapidly attracts the moisture of the breath, or 

 of the apartment. The diameter of the glass may be four 

 inches, the height of it eight inches. The size of the plate 

 at top from two to four inches, as most convenient. The 

 cap which incloses the top of the glass, and into which the 

 glass tube is cemented, may be of wood or metal. 



Price, $2.00. 



Volta's Condenser (Fig. 284) shows a pair of these con- 

 densing plates attached to a gold leaf electroscope. The 

 plate, A, is connected with the cap, and is of course insu- 

 lated. The plate, B, is supported upon glass, but is con- 

 nected with the ground by the chain ; it turns upon a joint 

 at c. It is sometimes connected with another condenser 

 when the plate B becomes insulated by taking off the chain. 

 The two plates have a thin coat of gum lac varnish on their 

 inner sides, to prevent contact, and in consequence entire 

 dispersion. To use the instrument, touch the cap or plate, 

 A, with the excited body, B being withdrawn, then approach 

 B to A, and touch A again ; it may afterwards be made to 

 touch a third or fourth time, or more, until the gold leaves 

 show signs of divergence. Price, $6.00. 



Fig. 285. 



fiennefs Electrical DouUer. (Fig. 285, as above.) This 



