640 MECHANICAL EFFECTS OF THE DISCHARGE. 



better to surround the plate by an insulating liquid, sucli as olive 

 oil or paraffin oil. Fig. 331 represents such an arrangement. A 

 small tumbler is perforated by two holes opposite to each other .^ 

 Corks are fixed into the holes through which the straight pointed 

 ends of two wires pass, which are bent into rings at the outer ends. 

 The points of the wires must be carefully adjusted until they are 

 exactly opposite to one another. The glass plate being slightly 

 warmed is introduced between the points, these are moved until 

 they touch the plate, and the insulating liquid is poured into the 

 tumbler until the latter is nearly full. Two chains connect the rings 

 with the external coating of the Leyden jar .and one knob of the 

 discharger respectively. The jar must be charged as strongly as 

 possible,. and the whole of the contrivance should be set up close to 

 the machine, in order to avoid the loss of electricity which would 

 occur if the jar had to be carried any distance. The jar maybe 

 arranged by suitable supports so that its knob may touch the small 

 brass ball of the conductor of the machine, and a chain which is 

 attached to one ring* in the apparatus for the perforation is wound 

 several times round the outer coating of the jar. The connection 

 of the other ring with one knob of the discharger is also made pre- 

 viously to charging the jar. All being thus in readiness, the dis- 

 charger is held in the left hand, the machine is worked by the right 

 until the jar is strongly charged, when the free knob of the dis- 

 charger is quickly brought near to the knob of the jar. When the 

 experiment succeeds there will be a fine hole through the plate, 

 from which usually several cracks spread in different directions. 



The mechanical perturbation of a liquid by the 

 discharge requires a very powerful charge of the jar or 

 battery used for the purpose. Insulating liquids 

 scarcely permit the passage of the discharge ; water is 

 therefore generally used for the experiments. A dis- 

 charge which takes place in water between the opposite 

 ends of two wires separated by a considerable distance 

 is retarded and weakened, for water, although a con- 

 ductor, is a worse conductor than metals, and as the 

 electricity has in this case to traverse a great ' distance, 

 the effect of the inferior conductivity of water upon the 

 discharge becomes appreciable. But if the wires are 



