Page:Popular Science Monthly Volume 33.djvu/102

92, which were conveyed from the water by a cylindrical tube of tin some nine feet long and six inches in diameter, one end of which terminated in an orifice for insertion in the ear, and the other was spread out somewhat in the form of a spoon, its opening being closed by a flat, elliptic plate of tin, about two square feet in area. By attaching a suitable weight to the lower end of the tube it was easily retained in a vertical position with about four fifths of its length submerged, its flat plate being turned toward the boat carrying the bell. With this simple apparatus, Colladon was able to hear with perfect distinctness the blows of the hammer on the bell across the widest part of Lake Geneva, when the calculated distance between the two boats was not less than eight miles.

The sounds heard by Colladon appeared as if they had been caused "by some metallic body striking the bottom of the tube," and they were "as distinct and brief at 13,000 metres as at 100 metres from the bell." One set of observations were made during a strong wind: "The lake, which was at first calm, became violently agitated, and it was necessary to keep the boat in position by means of several anchors; yet, in spite of the noise of the waves which struck the tube, he took other observations with the same accuracy as when the air and water were still. And he states,"I am convinced that by employing a bigger bell, and improving or enlarging the hearing apparatus, easy communication could be effected under the water of a lake or of the sea up to fifteen or twenty leagues."

In February, 1883, Prof. Lucien I. Blake, now of the University of Kansas, but then in Berlin, while investigating the experiments of Colladon and also of Sturm, as to the velocity of sound through the waters of Lake Geneva, thought of making a practical use of water as a means of communication between vessels at sea. He then devised several methods, assisted by Dr. König, of the Physical Laboratory at the Royal University, which he tried on his return to this country, and he has been experimenting in that direction from time to time since that date, as opportunity served.

His plan, in brief, was as follows: A sound-producing apparatus was to be attached to each vessel, and to be worked under the surface of the water. In times of fog or at night a code of signals would be produced by it which would be transmitted in all directions through the water, with a velocity four to five times that in the air. Each vessel, in addition to the sound-producing apparatus, would be provided with a sound-receiving apparatus,