The World's Advance, August, 1915, pages 268-269:
The Danger of Hertzian Waves
By B. S. Blakee
THE discharge of an electric spark is the source of radiant energy capable of producing at a distance upon an electrical apparatus called a "resonator" powerful vibratory movements which are liable to give rise to other sparks. This phenomenon was first observed by the German physician Hertz, by means of a metallic circle cut in such a way as to leave the free ends close together, placed in an oscillating field of induction. This principle has been made use of recently in England to cause an explosion in the hull of an old ship lying at some distance from a wireless station. The details of the operation have been kept secret, but a similar experiment may be made with the following simple apparatus:
Fill a glass flask with an explosive mixture of oxygen and hydrogen (two volumes of H to one of O) and close the mouth of the flask with a stopper of paraffin through which have been pushed two steel needles with blunt and polished points, so that they approach at an angle and leave a small space between the ends. Now connect the needles to long insulated wires, which may be extended to the earth or hung on brackets in opposite directions. If operated in stormy weather, or in the neighborhood of a wireless station, one will not have to wait long for a spark induced by an electric wave, which will cause the explosion of the gases with a report like the crack of a pistol.
This experiment of the English Admiralty is probably the first in which these waves have been voluntarily used to cause destruction, but it is not certain that the destroyed ship is the first victim of electric resonance.
The accidental occurrence of the Hertzian experiment is perhaps more common than is imagined, on account of the numerous resonators which chance leaves in the paths of the electric waves. It is only necessary that such conditions be present in an inflammable medium to cause a fire.
M. Duroquier, writing in La Nature, says that he would be sorry to cause unnecessary alarm to sailors, miners and aeronauts, but the memory of recent catastrophes in which many lives have been lost leads one to believe that special care should be taken under certain conditions and in certain localities to counteract the effects of the electric waves which reach to the depths of a mine as readily as they reach a ship at sea or a dirigible balloon in the air.
On board ship some chain, or perhaps scrap iron in the coal bunkers may cause sparks which will start a fire. In the case of a battleship, shells lying close together in a badly ventilated ammunition vault may be exploded by the same means. To cause the firing of a dirigible, all that is necessary is the formation of sparks across some gap in the metallic frame-work.
Numerous instances may be cited of the inductive effects of these waves. At the wireless post at Mont-Valerien, several miles from Paris, the emissions from the Eiffel Tower give rise, by resonance, to sparks several millimeters in length at the point of the detectors on the receiving table. On shipboard, also, this effect can be observed in the metallic rigging when the wireless is in operation.
Continuing, M. Duroquier says that the dangerous effects of induction are to be feared not only under a storm cloud, or near a radio-telegraphic station, but especially at points halfway between two powerful stations. He noticed that at his own wireless station some of the delicate instruments were frequently out of order from some unknown cause and by drawing a straight line on a map from Paris to the nearest wireless station, situated at Rochefort, he found to his astonishment that his own station is just midway between the other two. By connecting the various large stations in Europe and America, he made the further discovery that halfway between Glace Bay and Paris is the region in which the Volturno took fire; that halfway between Paris and Bizerte on the north coast of Africa, is the harbor of Toulon, where explosions have occurred on a number of French warships; and that halfway between Paris and Clifden, Ireland, is Cardiff, at which disastrous mine explosions have taken place in the recent past.
Possibly the recent burning of a Zeppelin airship may be put down to the same cause, but in any case it would seem wise to take special precautions against fire in these localities.