238 HENKY A. ROWLAND 



Lieutenant FISKE. I would like to ask how far lightning obeys the 

 ordinary law of currents, whether it takes the path of least resistance 

 or not. Do high potentials always do that? In general across a nar- 

 row space the resistance is greater than going around by the iron, and 

 the question is, to what extent does the lightning obey the law of 

 circuits ? 



Professor ROWLAND. I would like to say one word more with respect 

 to petroleum. In the case of the tank you have a mixture of the petro- 

 leum vapor and air which probably would explode. Unless the tank was 

 a very good conductor there might be also a little spark in the interior, 

 not enough to hurt a man in there; but the smallest spark inside the 

 tank would cause an explosion. I am not certain whether the iron of 

 the tank is a good enough conductor to prevent every trace of spark in 

 the interior. Indeed, suppose we had a tank with a cover upon it. 

 That is supposed to be a closed vessel, yet the lightning would have to 

 pass from top to bottom between the cover and the tank, and perhaps 

 a little spark would take place in the interior; and possibly in going 

 from one of the plates of the iron tank to the other it may find some 

 resistance and jump over some small plate in the interior of the tank. 

 It would be a most difficult thing to protect. 



With regard to that other question, lightning in the air, of course, 

 does not obey Ohm's law; it is entirely a discontinuous anomaly. It is 

 like the breaking of a metal. A piece of metal is supposed to break at 

 a certain strain; but it does not always break then; it pulls out in 

 strings or something of that sort. One cannot measure the distance 

 and say the lightning is going to jump across that distance. 



