THUNDER AND LIGHTNING. 



and at f it is simply secured by bolts to a horizontal beam 

 through which it passes. The last is evidently the least solid 



method of fixing it. 



Fig. 3. 



i 



The conductor is continued downwards along the wall of the 

 edifice, or in any other convenient course, to the ground, either 

 by bars of iron, round or square, or by a cable of iron or copper 

 wires, such as is sometimes used for the lighter sort of suspension 

 bridges. This is attached, at its upper extremity, to the base of 

 the paratonnerre by a joint, which is hermetically closed, so as to 

 prevent oxidation, which would produce a dangerous solution of 

 continuity. 



To comprehend the protective influence of this apparatus, it 

 must be considered that the inductive action of a thunder-cloud 

 decomposes the natural electricity of the rod, more energetically 

 than that of surrounding objects, both on account of the material 

 and the form of the rod. The point becoming surcharged with 

 the fluid of a contrary name from that of the cloud suspended over 

 it, discharges this fluid in a jet towards the cloud, where it 

 combines with and neutralises an equal quantity of the electricity 

 with which the cloud is charged, and, by the continuance of this 

 process, ultimately reduces the cloud to its natural state. 



It is therefore more correct to say that the paratonnerre draws 

 electricity from the ground and projects it to the cloud, than that 

 it draws it from the cloud and transmits it to the earth. 



It is evidently desirable that all conducting bodies to be pro- 

 tected by the paratonnerre, should be placed in metallic connection 

 with it, since in that case their electricity, decomposed by the 

 inductive action of the clouds, will necessarily escape by the 

 conductor either to the earth or to the cloud by the point. 

 186 



