306 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 3G4. enc [ ri n httle j^ij mac [ e O f pith ; the other ends 

 of the wires being suspended from a cork, which 

 is rather long and tapering at both ends, so as to 

 fit either way into the mouth of a varnished glass 

 tube, serving both as a handle to the instrument 

 when in use, and as a case for it when carried in 

 the pocket. When it is to be employed as an 

 electroscope, the cork is so placed that the wires 

 hang out of the tube, and will indicate by their 

 divergence any electricity that may be communi- 

 cated to them. When not in use, reversing the 

 cork closes up the instrument, and renders it more 

 portable. Price, $0.50. 



Fig. 33.5. Coulomb's Tortion Balance. (Fig. 365.) 



a . This delicate contrivance consists of a 



thread of silk, a b, from which a needle of 

 shellac, c, is suspended ; it is attached to 

 the screw, d, by which it can be twisted 

 round its axis ; the needle carries a ball of 

 pith gilt, which is balanced by a counter- 

 poise on the other ; e is a metallic wire 

 passing through the glass shade, and ter- 

 minated by a metallic ball at each end ; the 

 ball of the needle and the interior brass 

 ball of the wire are brought into contact 

 by turning the screw, d, and the index 

 then points to the o on the scale, which is 

 marked on the circumference of the glass. 

 When the ball, e, is electrified, it acts on the 

 ball within that is attached to the needle, 

 repelling it to a certain distance, which 

 distance, and consequently the degree of 

 electrization, is indicated by the graduated scale. 



Price, $12.00. 



The Dry Pile, or Electrical Chime. (Fig. 366, next 

 page.) This instrument consists of a number of alternations 

 of two metals, with paper interposed ; the elements may 

 be circular discs of thin paper, covered on one side with 

 or silver leaf, about an inch in diameter, and similar 



