December 17, 1909] 



SCIENCE 



859 



greater." Then further he says: " This 

 light and crackling seems in some degree 

 to represent thunder and lightening." I 

 believe this to be the first reference to the 

 possible relationship between electricity 

 and lightning. The later historj' of Frank- 

 lin's suggestion of identity, D'Alibard's 

 experiment and that of the famous kite 

 furnishing experimental proof, are too well 

 known to be dwelt upon here. 



The practical genius of Franklin led him 

 at once to the suggestion of protection from 

 lightning by mean.s of a conducting rod of 

 metal, well connected to the moist ground 

 at its lower end, and projecting beyond the 

 highest parts of the building or structure 

 to be protected. In these later years it is 

 not unusual to meet with statements of dis- 

 credit or denial of the efficacy of this simple 

 device. There seems to be a tendency 

 among the uninformed to regard it as an 

 old-fashioned and useless if not a dangerous 

 contrivance. Often the question has been 

 asked whether it is not an exploded notion 

 that such rods have any value for protec- 

 tion. It may well be that the "lightning- 

 rod agent" of former times is largely re- 

 sponsible for the distrust. He was a sort 

 of confidence man, who supplied a sham 

 appliance, often of marvelous makeup. A 

 structure of twisted metal tube topped with 

 glittering gilt points in clusters, mounted 

 on green glass insulators, the whole as ex- 

 tensive as the unhappy victim could be 

 frightened into paying for, was erected, 

 and often left without any adequate con- 

 nection to the ground. It was a tree with- 

 out roots; lacking, in fact, the most essen- 

 tial part of its structure. 



Let us add with emphasis that the Frank- 

 lin rod when properly installed undoubt- 

 edly secures practical immunity from light- 

 ning damage. Its installation is an engi- 

 neering undertaking demanding study of 

 varied conditions and proper care and 



judgment in meeting these conditions. The 

 one consideration originally left out was 

 that if there were any better or more direct 

 paths for lightning existing in the building 

 or structure or better ground connections 

 than the rod possessed these must be in- 

 cluded in the protective system. But it is 

 also a fact that the construction of mosf 

 modern buildings, particularly in cities, in- 

 volves so much metal in roofing, ventilating 

 and other pipes, wires and the like, that it 

 is generally unnecessary to resort to any 

 separate means for protection. 



In cities there are many lofty structures 

 framed in steel, piping that projects above 

 the roof, and metal stacks, generally in 

 good connection with the underground pipe 

 systems ; all of which together tend to mini- 

 mize danger from strokes of lightning. 

 The best vindication of Franklin will, how- 

 ever, be found in the fact that the firmest 

 reliance is placed by the trained electrical 

 engineer upon the provision of an easy 

 path for the electricity of lightning to 

 reach the ground. Practically all his pro- 

 tective appliances or arresters used in elec- 

 tric systems are based on that principle, 

 with modifications and additions to suit 

 particular conditions of use. To provide 

 such modifications and adaptations is 

 by no means an easj' task. There is still 

 a possibility of insufficiencj'' such that 

 the menace of breakdowns and damage 

 by lightning still remains a hete noir to the 

 engineer. The tremendous discharge of 

 energy possible in a lightning stroke may 

 be sufficient to defeat our efforts. Break- 

 ing through insulation and causing short 

 circuits, burning of wires and rupture of 

 circuit, and damage to apparatus are still 

 occasional experiences in spite of our safe-, 

 guards. Even at a considerable distance 

 away a stroke of lightning, by its inductive 

 action may set up electric waves or surg- 

 ings which require to be provided against. 



