ELECTRICAL APPARATUS. 



291 



alls in high latitudes. To insure success, the tube should be 

 thoroughly dried previous to use, to free it from all damp- 

 ness. 



This apparatus is also commonly used for showing the 

 guinea and feather experiment in pneumatics, having a piece 

 of metal and feather within the tube. 



Price, three sizes, $4.50 ; $6.00; $10.00. 



Aurora Flask. (Fig. 333.) This consists of a Fig. 333. 

 glass flask, holding about a quart, coateil with tin 

 foil at the end of the globular part, covering about 

 one-third of the sphere to the neck. There is ce- 

 mented a brass cap, with screw, for attaching to 

 the air-pump, and having a valve on the end of the 

 screw to prevent the return of the air, over which 

 a nut is screwed to prevent any leakage. To imi- 

 tate the aurora borealis make the flask very hot 

 before the fire, hold it by the tin foil, and hold its 

 ball to a charged prime conductor. Very long and 

 brilliant flashes will pass along the partly exhaust- 

 ed flask. The flashes will continue long after the removal 

 of the tube from the machine. Price, $2.50. 



Fig. 334. 



The Luminous Discharger. 

 (Fig. 334.) This consists of 

 a bent glass tube, having a 

 brass ball at each end, con- 

 nected by an iron chain which 

 passes through the tube, and 

 having a wooden handle. 



Discharge any Leyden jar 

 with this discharging rod, and 

 it will appear beautifully lu- 

 minous. Price, $2.00. 



Spiral Tube.(F\g. 335, next page.) This consists of 

 two glass tubes, placed one within the other. On the 

 outside of the inner tube are fastened spangles of tin-foil ; 

 the two ends of the tubes are wrapped round with tin-foil, 

 and cemented each into a brass cap. To use the spiral 

 tube, hold one end in the hand and the other apply to the 

 conductor, when a spark will pass along the whole length. 



Price, $2.00 and $2.50. 



