418 



NEGRETTI AND ZAMBRA, HOLBORN VIADUCT, E.C., 



FIG. 2411* 



FIG. 2418. 



FIG. 2417. 



FIG. 2420. 



2410 Balance Electrometer, or Electroscope, very simple and delicate. It consists 



of a light metal rod suspended on a point, insulated on a glass stand. 

 The rod is mounted with pith balls on each end, which will be attracted 

 or repelled according to the quality of the electricity affecting it 11 



2411 Bennet's Gold Leaf Electroscope (Ginger's improved 



form) : used for showing very minute quantities of 

 electricity (fig. 2411). See also page 115 . . .110 1 10 

 2411* Cavallo's Pith Ball Electroscope 110 



2412 Volta's Condensing Electroscope (fig. 2412), see page 425. 1 10 



2413 Henly's Quadrant Electrometer, with graduated arc, for 



experiments with accumulated electricity (fig. 2413) . 



2414 Cavallo's Pith Ball Electroscope, with stopcock for 



exhaustion (fig. 2414) 



2415 De Luc's Electric Column or Pile, composed of discs 



of silver, zinc, and paper, mounted glass tubes with 

 brass caps at the ends 



2416 Zamboni's Electric Pile. The elements in this pile are 



silver, black oxide of manganese, and paper, insu- 

 lated with sulphur : it is more energetic than De Luc's ; 

 mounted in glass tubes, terminated with brass caps . 



2417 Bohenburger's single leaf Electroscope, for ascer- 



taining the presence and quality of very feeble 

 electrical currents (fig. 2417). See page 116 



2418 Peltier's Electrometer (or Dr. J . Milner's, 1733) for mea- 



suring the tension of electricity by the deflection of a 

 needle ; an extremely sensitive instrument (fig. 2418) 



2419 Harris's Balance Beam Electrometer, for estimating in 



grain weights the attractive power exerted between 



two oppositely electrified surfaces .... 440 



076 1 10 6 



220 



1 14 330 



1 10 330 



440 550 



