ox TRANSMISSION 01' SOUND-SIGNALS UNDER WATER. 213 



them lias been given by Professor Hennessy in a Report, printed in the volume 

 of the Eeports of the Association for 1801*. 



If these experiments should lead to an available means of communication 

 between two ships in company at sea, or between a ship and the coast during 

 foggy weather, an important purpose would be accomplished. 



At first the attention of the Committee was directed to repeating M. Col- 

 ladon's experiments, substituting for the bell he employed cyHndrical bars of 

 steel, from 6 to 8 feet in length, and from 1 inch to 1| inch in diameter; 

 these were supported on, or suspended from, their nodal points, and struck 

 ■with hammers of different weights at one of their ends, so as to excite them 

 longitudinally. These experiments were made in the large water-trough of 

 the Polytechnic Institution, and subsequently in the ornamental waters of the 

 Eegent's Park : the available distance in the former case was about seventy 

 yards, in the latter about half a mile. Employing CoUadon's ear-trumpet, 

 the sounds were very distinctly heard, and even at the short distance in the 

 Polytechnic, the sounds through the air were separated from those heard 

 through the water by a distinct interval. The character of the sound was, 

 however, very different in the two cases ; that transmitted through the water 

 being more abrupt, though in both cases they were mere blows or impulses, as 

 the method of excitation was not intended to produce continuous musical 

 sounds. Though the sounds were not of a character produced by any musical 

 instrument, yet a pitch could be recognized in them in the same manner as a 

 pitch can be perceived in blows made at different parts of a table. By select- 

 ing two bars of different lengths, the sounds produced by each might be com- 

 bined in the different orders of succession, which constitute the telegraphic 

 alphabet. We did not extend these experiments further on account of the 

 expense which would be incurred by the purchase of a sufficient number of 

 bars to enable us to ascertain the best dimensions for the effective production of 

 the required sounds, and also in the expectation that we might, by the opera- 

 tion of some members of the Association, obtain the temporary loan of such 

 materials. 



Professor Hennessy, who resides on the sea-side, near Dublin, is willing to 

 undertake such further experiments as would be required for testing the 

 application of sound-signals in extensive spaces out at sea. On this point Dr. 

 Gladstone has already made a few experiments at Eastbourne. He and his 

 children had taken two boats when there was considerable movement on the 

 surface, and the sounds were produced from one boat while they were listened 

 for from the other. Musical sounds appeared to be immediately stopped, while 

 a blow struck end ways on an iron bar could bo heard at a great distance. 



Soimds produced in the air did not seem to penetrate through the water ; 

 but the sound of breaking waves on the shingle of the shore was distinctly 

 heard throiigh the water. This noise heard through the water resembled a 

 series of sharp ticks, and could be easily distinguished at a considerable dis- 

 tance. The detection of this kind of sound is manifestly interesting with 

 reference to the guidance of vessels approaching a coast during the prevalence 

 of a fog. Such noises, though extinguished in their passage through air 

 during a fog, would still be transmitted through water, so as possibly to act 

 at certain parts of the coast as a natural fog-signal. 



The attention of the Committee has been specially directed to the produc- 

 tion of musical sounds under water. The instruments which appeared to be 

 most available for this purpose were Cagniard de la Tour's Syren, and pipes 

 or whistles, in which the vibrations were caused by currents of water in masses 



* Thirty-first Eepcrf, p. 173. 



