560 



THE POPULAR SCIENCE MONTHLY 



such as have been advocated by the various 

 farmer organizations, and concentrate their at- 

 tention upon the one overmastering issue of 

 the tariff. It has long been recognized that 

 the ultimate disposition of the tariff question 

 lies with the farmers. They constitute forty 

 per cent of those engaged in gainful occupa- 

 tions, and in the very nature of their occupa- 

 tion can not be benefited by the tariff while 

 the cost of nearly everything they buy is en- 

 hanced by it. Whenever they thoroughly real- 

 ize that the tariff is a tax and is paid by the 

 consumer, that the current appeals of pro- 

 tectionists are the merest sophistries, they 

 have it in their power to make very short 

 work of this antiquated system. There are 

 not wanting signs that a good many farmers 

 are coming to a sense of the real state of the 

 case, and books like that of Mr. Strange can 

 not but help them to reach rational conclu- 

 sions. 



Lightning Conductors and Lightning 

 Guards. By Oliver J. Lodge. London: 

 Whitaker & Co. New York : Macmillan 

 & Co. 1892. Pp. 544. Price, $4. 



This volume is a discussion of the sub- 

 ject of lightning protection, in view of the 

 recent advances which have been made in 

 our knowledge of currents of high potential 

 and high frequency. It contains two lec- 

 tures before the Society of Arts, as well as a 

 number of miscellaneous papers upon the 

 general subject. Prof. Lodge takes excep- 

 tion to the current view that conductivity is 

 the main thing to be considered in an effi- 

 cient lightning protector. Experiment has 

 shown that, even with lightning rods of 

 many times the conductivity necessary to 

 carry off a current of the dimensions of a 

 lightning stroke, the lightning refuses to fol- 

 low the conductor, and makes all sorts of 

 curious detours through paths of enormously 

 high resistance. This phenomenon, which is 

 inexplicable on the theory that a lightning 

 flash is simply a high-tension current for 

 which a conducting path must be provided 

 to assure its safe disposition, finds ready ex- 

 planation on Prof. Lodge's theory. He likens 

 the lightning discharge to a blow on the wa- 

 ter contained in a pipe. If the blow be quick 

 enough, the water will not be set in motion, 

 but the pipe will burst. The remedy is, not to 

 make the pipe larger, but to make it elastic. 



A lightning flash, in this view, is a disrup- 

 tive discharge between the opposite surfaces 

 of a condenser through the intervening di- 

 electic. The clouds form one surface of this 

 condenser and the earth the other, the in- 

 tervening air being the dielectic. It is now 

 well known that the discharge of a condenser 

 is alternating and of great frequency. The 

 discharge of a condenser of such a great ex- 

 tent of surface as that presented by the clouds 

 and the earth, Prof. Lodge maintains, must 

 be not only of enormous tension and fre- 

 quency, but of large current volume as well. 

 It is commonly stated that the amount of 

 current in a lightning discharge is very small 

 indeed, and this is quite true. The discharge, 

 however, occupies but an infinitesimal frac- 

 tion of time. If it were prolonged so as to 

 make it comparable with our standards of 

 current, the current flowing would be at the 

 rate of thousands of amperes per second. In 

 this view of lightning discharge, lightning 

 protection is not so simple a thing as has 

 generally been supposed. Instead of provid- 

 ing simply a drain for the electric fluid, light- 

 ning protection has to devise means for es- 

 caping a tremendous blow, delivered with 

 almost inconceivable rapidity. Happily, we 

 are not helpless in the presence of this re- 

 quirement. It has long been known that no 

 charge resides in the interior of a closed 

 metal chamber, no matter how strongly the 

 surface is charged. Such a chamber is, of 

 course, impracticable as a means of protec- 

 tion, but a metallic network will answer near- 

 ly as well and is practicable. Prof. Lodge's 

 practical suggestions, therefore, take the 

 form of multiple wires, all connected together 

 to form a large mesh network, and terminat- 

 ing at the roof in points. These points may 

 be roughly fashioned, as there is no practical 

 difference in protection between rough and 

 highly finished points. There is no advan- 

 tage in carrying the points high up in the 

 air, as this simply invites a discharge which 

 might not occur. Such a network, well 

 grounded, he conceives, will form ample pro- 

 tection in most cases. The wires used need 

 not be larger than ordinary telegraph wires, 

 and, as resistance is a matter of no moment, 

 iron will do as well as copper. The great im- 

 portance of adequate lightning protection 

 renders such a discussion of the subject as 

 Prof. Lodge has here given us of no little 



