42 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



parts of which every other house and barn is fitted with them, I cannot 

 learn that the fire insurance companies make much or any diminution 

 in their rates of premium on buildings so fitted. These remarks apply 

 to all kinds of lightning-rods. Whatever their construction, unless well 

 made and well kept, they are a source of danger, rather than of safety. 



But there is an element of danger in the Chambers rod, arising from 

 the principle on which it is constructed, that does not exist in the case 

 of the usual "earth-fast" rods. These latter act on the principle that the 

 air and the earth are always in opposite states of electric tension. Our 

 knowledge does not allow us to say if this is absolutely and necessarily 

 true, but experience shows that it is perfectly safe in practice to assume 

 that it is so. Consequently, the action of the rod depends on its 

 power of communicating by a continuous and infusible conductor be- 

 tween the one and the other, by which means the electric tension is 

 equalized, either by a slow and silent discharge, as commonly occurs, 

 or by a 'sudden and sharp flash. 



The Chambers rod, on the other hand, is constructed on the princi- 

 ple that different masses of air are also in different conditions of elec- 

 tric tension, and that these different masses of air are very near each 

 other. The first of these two principles is true beyond question. 

 This is proved by the constant i)assage of sparks or flashes of lightning 

 between cloud and cloud, or, more accurately speaking, between one 

 body of air and another, without "striking" the earth at all. Probably 

 this is by far the commonest mode of restoring the disturbed equilib- 

 rium. Not one flash, apparently, among hundreds that occur, strikes 

 the earth, or anything upon it. Were it .otherwise, so many storms 

 could not happen without any mischievous consequences. Compara- 

 tively seldom do we hear that anything or anybody has been struck by 

 one of the hundreds of electric flashes occurring during every summer. 

 They discharge themselves in the air. An overcharged mass relieves 

 itself by "flashing" into one with less tension at no great distance. So 

 far, the principles on which the Chambers rod is constructed are well 

 founded. 



But the second principle is open to grave suspicion, and this sus- 

 picion, to say the least, is a serious objection to the general adoption 

 of this system of "protection." In assuming that these masses of air 

 of unequal electric tension are in close proximity, the advocates of 

 this system claim more than can be granted. Without raising any 

 question of the meaning of the word "proximity," it is evident that it 

 must mean "striking distance," Now, that two masses of air of une- 



