166 Mr Harris on the Utility of fixing 



22. It will be found, however, that the action of pointed me- 

 tallic bodies is purely passive ; that they only afford by the apt- 

 ness of their parts an easy transmission to the electric matter ; 

 so that they can no more be said to attract the matter of light- 

 ning, than a dike can be said to attract the water which neces- 

 sarily flows through it at the time of heavy rain ; and, as in the 

 one case, the water is drawn down by a force not peculiarly ap- 

 pertaining to the dike, so, in the other case, the electric matter 

 is determined to a given point, in a somewhat similar way, by 

 a force not appertaining to the metal. Moreover, it may still 

 further be reasoned by analogy, that, as the quantity of water 

 transmitted will depend on the capacity of the dike, and the 

 final protection it gives in conveying the fluid on the length to 

 which it is continued ; so, on the other hand, the protection af- 

 forded by a lightning rod will also depend on its capacity, and 

 the distance to which it runs. If, in both cases, the length be 

 extended until the force in action be satisfied, the protection re- 

 ceived will be as the capacity for transmitting the current : if 

 both be perfect, the protection will be complete ; if the dike be 

 not present, the water must be supposed to run loose and undi- 

 rected ; or, if its continuity be frequently interrupted or nar- 

 rowed to a small compass, the damage must then be supposed 

 to happen in the intermediate spaces. Such is, in fact, the way 

 in which all bodies of the conducting class already mentioned 

 (4) operate in conveying electrical discharges ; and it must never 

 be forgotten as an important feature in this discussion, that, 

 whenever we erect an artificial elevation on the earth's surface 

 in the ordinary way, we do, in fact, set up a conductor of elec- 

 tricity, upon which the electricity of the atmosphere will fall, 

 and no human power can prevent it. Hence, if metallic bodies 

 be present, those will be first assailed ; if not, then the electric 

 matter will fall on the bodies next in conducting power, and 

 so on. 



23. A curious illustration of this principle will be found in 

 an extract from the Memoirs of the Count de Forbin, which is 

 given in the forty-eighth volume of the Philosophical Transac- 

 tions. " In the night," says the author of these memoirs, " it 

 became extremely dark, and it thundered and lightened dread- 

 fully. As we were threatened with the ship being torn to 



