LIGHTNING RODS 305 



well acquainted with the phases of human perversity if you can anticipate what I 

 am now going to tell you, namely, that this massive glass cap, or reseller, as it was 

 fondly called, was only a year or two ago taken off from the top of the lightning- 

 rod employed to protect an important public building. [The repeller was exhibited. 

 It resembled a very large soda-water bottle with a neck much wider than the usual 

 form.] From the experiments you have just seen it must be evident to you that 

 the two main requisites of an effective lightning-rod are that it should have a sharp 

 point (or, better, a number of such points, lest one should be injured), and that it 

 should be in excellent communication with the ground. When it possesses these, 

 it does not require to be made of exceptionally great section ; for its proper function 

 is not, as is too commonly supposed, to parry a dangerous flash of lightning: it 

 ought rather, by silent but continuous draining, to prevent any serious accumulation 

 of electricity in a cloud near it. That it may effectually do this it must be thoroughly 

 connected with the ground, or (if on a ship or lighthouse) with the sea. In towns 

 this is easily done by connecting it with the water mains, at sea by using the 

 copper sheathing of the ship, or a metal plate of large surface fully immersed. Not 

 long ago a protected tower was struck by lightning. No damage was done in the 

 interior, but some cottages near its base were seriously injured. From a report on 

 the subject of this accident it appears that the lower end of the lightning-rod was 

 "jumped" several feet into the solid rock! Thus we see, in the words of Arago, 

 how " False science is no less dangerous than complete ignorance, and that it 

 infallibly leads to consequences which there is nothing to justify." 



That the lightning-rod acts as a constant drain upon the charge of neighbouring 

 clouds is at once proved when there is, accidentally or purposely, a slight gap in 

 its continuity. This sometimes happens in ships, where the rod consists of separate 

 strips of metal inlaid in each portion of the mast. If they are not accurately 

 fitted together, a perfect torrent of sparks, almost resembling a continuous arc of 

 light is seen to pass between them whenever a thunderstorm is in the neigh- 

 bourhood. 



I cannot pass from this subject without a remark upon the public as well as 

 private duty of having lightning-rods in far greater abundance than we anywhere 

 see them in this country. When of proper conducting power, properly pointed, 

 properly connected with the ground and with every large mass of metal in a building 

 they afford absolute protection against ordinary lightning every single case of 

 apparent failure I have met with having been immediately traceable to the absence 

 of one or other of these conditions. How great is their beneficial effect you may 

 gather at once from what is recorded of Pietermaritzburg, viz., that till lightning- 

 rods became common in that town it was constantly visited by thunderstorms at 

 certain seasons. They still come as frequently as ever, but they cease to give 

 lightning-flashes whenever they reach the town, and they begin again to do so as 

 soon as they have passed over it. 



A knight of the olden time in full armour was probably as safe from the 

 effects of a thunderstorm as if he had a lightning-rod continually beside him ; and 

 one of the Roman emperors devised a perfectly secure retreat in a thunderstorm 

 in the form of a subterraneous vault of iron. He was probably led to this by 



T. 39 



