PROTECTION AGAINST LIGHTNING. 819 



ors of insufficient dimensions, and of bad principles of construction, 

 are by no means to be looked upon with tolerance, to say nothing of 

 favor, notwithstanding the occasional good service that may be en- 

 tered to their account. 



Irrespective of all theoretical considerations, and upon purely ex- 

 perimental and demonstrative grounds, it is possible in the present 

 state of electrical science to definitely state what it is that an electri- 

 cal engineer has to do when he undertakes to protect buildings against 

 the destructive force of lightning. He has, in the first place, to make 

 sure that, wherever the lightning can fall, it shall find an open and prac- 

 tically unobstructed path to traverse in its passage to the ground. He 

 is quite sure that the electric discharge will confine itself to the track 

 of a conductor, and will pass quietly and harmlessly along it, provided 

 its dimensions are adequate to the task of transmission, and provided 

 the inlets and outlets are sufficiently capacious for its unimpeded 

 reception and escape. It is a thoroughly established and altogether 

 indisputable canon of electrical science that when a discharge has to 

 pass through a conductor of too narrow size, and with obstructed inlets 

 and outlets, it, of necessity, accomplishes its passage as a turbulent 

 and ill-regulated force all the way, with a tendency at every step to 

 make a devious outburst or overflow ; and that when it passes through 

 a conductor of ample dimensions, and with unimpeded ingress and 

 egress, it is devoid of all erratic impulse, and traverses the appointed 

 channel as an obedient and well-trained power. The task of the en- 

 gineer, therefore, resolves itself primarily into so arranging his appa- 

 ratus as to keep the lightning in its well-ordered and harmless state 

 so long as it is in the close neighborhood of buildings that might be 

 injured by any uncontrolled outburst through a devious path. There 

 are three ways in which he can seek to accomplish this purpose. He 

 can multiply and, as it were, enlarge the gates of ingress by increasing 

 the number of his air-terminals and earth contacts through which the 

 discharge may have to be gathered into the conductor. He can aug- 

 ment the dimensions and the carrying capacity of the conductor, and 

 he can amplify the outlets of escape, whether in the direction of the 

 cloud or earth. Where these conditions have been properly secured, 

 there is not the most remote probability that the conductor will fail in 

 its appointed task. This is not a question that is now open to doubt. 

 It is as certain that the lightning will traverse a weU-arranged and 

 competent conductor, rather than the building to which this is attached, 

 as it is that the electric spark from the charged conductor of an elec- 

 trical machine will strike a brass ball and rod, and will not strike a 

 stick of sealing-wax or of dry wood, when these are presented side by 

 side. As a matter of fact it is sometimes imperfectly insulated tracts 

 of the surface of the earth that are inductively charged by the propin- 

 quity of an overhanging storm-cloud, and sometimes the overhanging 

 cloud that is inductively charged by disturbances originating in the 



