1874] WRITINGS OF JOSEPH HENRY. 383 



Another apparatus proposed to be used as a fog-signal was 

 presented for examination by the Marine Signal Company, 

 of Wallingford, Conn. It consisted of a curved tube of cop- 

 per nearly in the form of the letter C, and was supported on 

 an axis passing through the centre of the figure. An ordi- 

 nary bell-whistle was attached to each extremity of the tube, 

 the instrument being placed in a vertical position and 

 partly filled with water, then made to oscillate on its 

 centre of support. By this means the air was drawn in at 

 one end and forced out through the whistle at the other. 

 The motion being reversed the air was drawn in at the end 

 through which it had just made its exit and forced out 

 through the whistle at the other. By rocking the instru- 

 ment, either by hand or by the motion of the vessel, a 

 continued sound could be produced. The motive power 

 in the former case was muscular energy, and the experi- 

 ments which were made at this time, as well as all that have 

 been made subsequently, conclusively prove that the pene- 

 trating power of the sound for practical use as a fog-signal 

 depends upon the intensity of the motive energy employed. 

 No instrument operated through levers and pumps by hand- 

 power is sufficient for the purpose. 



• One of these instruments with two 4-inch whistles gave a 

 sound, (as indicated by the artificial ear,) the power of which 

 was about one-tenth of that of a steam-trumpet. It was 

 supposed however that this instrument would be applicable 

 for light-ships; and that if extended entirely across the vessel 

 and armed with whistles of large size, it would be operated 

 by the rolling of the vessel, and thus serve to give warning 

 in time of thick weather. But as it frequently happens that 

 fog exists during a calm, this invention could not be relied 

 upon to give warning in all cases of danger. Besides this, 

 the ordinary roll of a ship is not sufficient to produce a 

 hydrostatic pressure of more than five or six pounds to the 

 square inch, which is insufficient to give an effective sound. 

 It has however been proposed to increase the power by using 

 quicksilver instead of water; but besides the first cost of this 

 material, and the constant loss by leakage and oxidation, 

 the tendency to affect the health of the crew is an objection 



