Electricity. 107 



with the inner coating of the jar. To discharge 

 the phial, a communication must be made (either 

 by what electricians call a conducting or dis- 

 charging rod D, or any other fit instrument) be- 

 tween the inner and outer coating of the jar. Its 

 effects may be proved by placing the phial or jar 

 (fig. 39.) on an insulated stand, bringing the 

 coating in contact with the conductor, and then 

 turning the machine. If in this case we apply 

 the discharging rod D, we shall find there will 

 be no explosion, because both sides being insu- 

 lated, the phial was not charged ; but if a small 

 chain is suspended from the brass knob of the 

 phial, and communicates with the table, the 

 phial will then be charged, and the explosion 

 will be considerable. The reason of this has 

 been explained before, as it was proved that the 

 electrical matter is derived from the earth. 



The shock which is given by the Leydcn phial 

 is much more powerful than that from the largest 

 conductor; but this power is greatly increased 

 by uniting together the force of several jars, in 

 what is called an electric battery (see fig. 40.). 

 The bottom of the box in this apparatus is co- 

 vered with tin-foil, to connect the external coat- 

 ings of the jars ; and the inside coatings are con- 

 nected by the wires a, &, c y d, e,j\ which meet 

 in the large ball above, There is a hook at the 

 bottom of the box, by which any substance may 

 be connected with the outside coating of the 

 jars ; and a ball B proceeds from the inside, by 



