Page:Popular Science Monthly Volume 33.djvu/107

Rh This method is also used to some extent by steamers on the great rivers. And it is practiced on the Great Lakes to some extent, notably at a certain bluff jutting out into Lake Superior. Passing steamers, knowing themselves to be in the vicinity, when befogged, feel out these bluffs by sounding their fog-signals until they get back an echo; then they use the bluffs as a new point of departure.

In this connection I may say that in the summer of 1886 I experimented in making echoes while on a lighthouse steamer on Long Island Sound, and found I could get a good echo by sounding the whistle of my steamer when passing a sailing-vessel, preferably a schooner, on a parallel course. Wave-sounds striking her sails at right angles to her course, gave a good echo at five hundred yards or less, and the sound of the echo was more or less good within that distance, in proportion to the angle made by the courses of the two vessels when their courses were not parallel. When off Block Island cliffs, which overhang somewhat, I got a good echo when about a mile distant. Hence I infer that the position of suspected dangers of certain kinds can be determined by the production of echoes under specified circumstances.

Recent papers state that Mr. H. B. Cox, an electrician whose laboratory is at Fernbank, some ten miles from Cincinnati, has invented a trumpet to be used for telephoning at sea, on which he has been at work for some months. The invention is the outgrowth of his discovery of the great distance an echoed or reverberated sound will carry, and the discovery that speaking-trumpets, if made to give the same fundamental note, would vibrate and produce the phenomenon known in acoustics as "sympathy."

With this trumpet conversation in an ordinary tone of voice was carried on between parties four and a quarter miles apart. People a mile away, conversing in an ordinary tone, could be distinctly heard, and in two instances they were told the nature of their conversation, and admitted that such had taken place. The whistle of a train was traced beyond Fernbank to Lawrenceburg, Ind. It was found that the instrument has a well-defined range of twenty-six miles; that is, a loud sound like a locomotive-whistle, or the rumbling of a train, can be distinctly heard at a distance of thirteen miles in every direction. Conversation was readily carried on between two gentlemen on high hills on opposite sides of the Ohio River distant about four and a half miles apart. Tests made on the water, of various kinds, showed that the trumpet was even more available than on land.

It is generally understood that Mr. Edison, who has invented so many good things, is now at work, and has made promising