ELECTRICAL APPARATUS. 301 



together. The electricity of e induces a change in the elec- 

 tric state of d c. Price, japanned tin, $2.00. 



" brass, $2.50 to $3.50. 



Set of three Conduct- Fi e- 



ors for Experiments on 

 Induction. (Fig. 355.) 

 This arrangement con- 

 sists of three conductors 

 mounted on glass pillars, 

 with mahogany stands ; 

 the conductors are form- 

 ed of brass, or japanned tin, with well rounded ends. These 

 instruments, when excited either by the proximity of a charg- 

 ed conductor, or by an excited glass rod held towards them, 

 beyond the conductor, N, draw away the central conductor, 

 and also the excited rod ; the central conductor, o, Vvill not 

 be charged at all, that marked P will be positive, and that 

 at N negative. 



When charged as before, as soon as o is removed, place 

 the conductor, N, so as to touch p. The disturbance of 

 both will be neutralized by each other, showing that the 

 quantity which is plus in one, exactly counterbalances that 

 which is deficient in the other. 



Price, $3.00 ; $5.00 ; and $8.00. 



The Double Jar. (Fig. 356.) To the knob Fi s- 336. 

 of a large Leyden jar a metallic stage, c, is 

 adapted on which is placed a smaller Leyden 

 jar. This instrument is used for various ex- 

 periments, and shows how necessary it is to 

 connect the outside and inside of the same jar 

 together, before it will be discharged. Place 

 the double bottle on a table not insulated, and 

 charge the upper bottle, A, positively, by con - 

 necting its ball with the conductor. The out- 

 side of A, therefore, and also the inside of B 

 will be negative, and the outside of B positive. 

 Now connect by the discharging rod the outer 

 coating of B with the inner coating of A, and 

 no shock will pass between them. Again, 

 connect the outside of B with the inside of B, 



