462 THE POPULAR SCIENCE MONTHLY. 



the need of a rod. In some localities rods are imperative ; in 

 others, needless. 



3. The very best ground you can get is, after all, for some 

 flashes, none too good ; therefore do not imagine that you can 

 overdo it in making a good ground. For most flashes ordinary 

 " grounds " suffice ; but the small resistance of even one ohm may 

 be dangerous with an intense flash. 



4. " If the conductor at any part of its course goes near water 

 or gas mains it is best to connect it to them. Wherever one metal 

 ramification approaches another it is best to connect them metal- 

 lically. The neighborhood of small-bore fusible pipes and indoor 

 gas pipes in general should be avoided." — Lodge. 



5. The top of the rod should be plated, or in some way pro- 

 tected from corrosion and rust. 



6. Independent grounds are preferable to water and gas mains. 



7. Clusters of points or groups of two or three along the ridge 

 rod are recommended. 



8. Chain or link conductors are of little use. 



9. Area of protection. Very little faith is to be placed in the 

 so-called area of protection. 



10. Indifference of lightning to the path of least resistance. 

 Nearly every one who has written in late years has taken it for 

 granted that lightning always follows the path of least resistance. 

 This is not true. " It is simply hopeless to pretend to be able to 

 make the lightning conductor so much the easier path, that all 

 others are out of the question," says Lodge. This, however, re- 

 quires modification. For the path will depend largely upon the 

 character of the flash ; and without doubt, for almost all flashes, 

 a good lightning rod well earthed is the most appropriate path to 

 earth. 



11. Any part of a building, under certain conditions, may be 

 struck, whether there is a protector on it or not. There are cases 

 on record where edifices seemingly amply protected have been 

 struck below the rods (not cases of defective connection), and it is 

 now beginning to dawn upon us that (paradox of paradoxes) a 

 building may be seriously damaged by lightning without having 

 been struck at all. The Hotel de Ville, at Brussels, perhaps the 

 best protected building in the world against lightning, was dam- 

 aged by fire, caused by a small induced spark near escaping gas. 

 During the thunderstorm some one flash started up " surgings " 

 in a piece of metal not connected in any way with the protective 

 train of metal. " The building probably did not receive," says Dr. 

 Lodge, " even a side flash, yet the induced surgings set up in it 

 were so violent as to ignite some gas and cause a small fire." In 

 other words, we had the condition of an " oscillator " in the cloud- 

 flash-earth and a " resonator " that responded with its little spark. 





