Page:Popular Science Monthly Volume 42.djvu/578

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THE POPULAR SCIENCE MONTHLY.

such as have been advocated by the various farmer organizations, and concentrate their attention 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 occupations, and in the very nature of their occupation can not be benefited by the tariff while the cost of nearly everything they buy is enhanced by it. Whenever they thoroughly realize that the tariff is a tax and is paid by the consumer, that the current appeals of protectionists 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 conclusions.

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 subject 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 lectures before the Society of Arts, as well as a number of miscellaneous papers upon the general subject. Prof. Lodge takes exception to the current view that conductivity is the main thing to be considered in an efficient 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 follow 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 explanation on Prof. Lodge's theory. He likens the lightning discharge to a blow on the water 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 disruptive discharge between the opposite surfaces of a condenser through the intervening dielectic. The clouds form one surface of this condenser and the earth the other, the intervening 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 extent of surface as that presented by the clouds and the earth, Prof. Lodge maintains, must be not only of enormous tension and frequency, 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 fraction 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 providing simply a drain for the electric fluid, lightning protection has to devise means for escaping a tremendous blow, delivered with almost inconceivable rapidity. Happily, we are not helpless in the presence of this requirement. 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 protection, but a metallic network will answer nearly 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 terminating 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 advantage 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 protection 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 importance of adequate lightning protection renders such a discussion of the subject as Prof. Lodge has here given us of no little