Page:Popular Science Monthly Volume 91.djvu/379

 �The Ben Franklins of Today

They study lightning with the camera " and at last they have told us what it is and by what it is caused

��Lightning striking the steeple of the First Presbyterian church of Greensboro, North C arolina

��the most important part — the earth termi- nal. The majority of the lightning con- ductors in America are consequently un- trustworthy. Unhappily these traveling impostors are by no means extinct, al- though increased knowledge is gradually driving them out of the field." Besides, the construction of the rod itself has

THE recent progress of knowledge undergone improvement, concerning lightning has far out- Scientific progress in the study of

stripped the ordinary reference books, lightning is due, to a great extent, to Thanks to Benjamin Franklin and his photography. Early investigators, such famous kite, our great-grandfathers knew as Arago, Dove and especially O. N. that lightning is an electrical discharge, Rood, had reached the conclusion that and they were also familiar with the many lightning flashes are multiple, con- lightning-rod. These gentlemen, however, sisting of several successive discharges supposed that lightning commonly occurs along an identical path, and had also in zigzags, with sharp angles, and not until formed a rough idea of the time intervals photography was applied to the study of involved. Various forms of rotating disk

��the phenomenon (about thirty-five years ago) was this erroneous no- tion dissipated. Our immediate ancestors — in this country, at least — had like- wise learned to view the light- ning-rod with considerable sus- picion. Early in the nineteenth century thou- sands of defective rods were erected by ignorant or unscru p ulous itinerant "light- ning-rod men," whose names have become a by-word among

���The flash seen to the left of the steeple was virtually instantaneous. That at the left of the chimney is a multiple flash, lasting for a fraction of a second

��were used in their experiments. Far more accurate in- formation on this subject is now obtained by the use of a camera mounted on a vertical axis and swung in a wide arc, at a fixed rate, by means of clockwork. This method has been gradually evolv- ed from the crude process of merely holding the cam- era in one's hands and giving it a side-to-side mo- 1 tion — the method followed by Trouvelot since the year 1888

��us. These persons, to quote a recent and by Weber and Hoffert in 1889. The authority, "used all kinds of fantastic perfection of the moving camera is due, in and peculiar shaped terminal rods and con- part, to Larsen, in America, but especially ductors, the main object apparently being to Dr. B. Walter, of Hamburg, whose to make as great a show with as little achievements in the photography of light- material as possible. Their work is almost ning far surpass those of any other in- entirely confined to the upper portion of vestigator. the conductor, to the absolute neglect of Walter began by photographing, with

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