488 WRITINGS OF JOSEPH HENRY. [1877 



buoy is a large tube or hollow cylinder three feet in diameter, 

 extending from the top through the bottom to a depth of about 

 thirty feet below the latter. This tube is open at the bot- 

 tom, but projects air-tight through the upper part of the 

 buoy, and is closed with a plate having three orifices in it, 

 two for letting in the air into the tube, and one between the 

 others for letting it out to operate the whistle. These orifices 

 are connected with three tubes which extend downward to 

 near the level of the water, where they pass through a 

 diaphragm which divides the cylinder into two parts. 



When the buoy rises, the water in the cylinder by its 

 inertia retains its position, and a partial vacuum is formed 

 between the head of the column and the diaphragm, into 

 which the air is drawn through two of the tubes, and when 

 the buoy descends, the escape through the injection tube 

 being prevented by valves, the air is forced out of the inner 

 tube and actuates the whistle. 



The mooring-chain, which is sixty fathoms in length, is 

 attached to the cylinder at a point just below the buoy, and 

 is secured to a large stone weighing about six tons. The 

 apparatus rides perpendicularly. 



The sound in this instrument is not produced merely by 

 the difference in hydrostatic pressure of the water in the 

 two positions of the buoy, but by the accumulated effect of 

 impulse generated by the motion of the apparatus. 



Plans have been devised — but have not yet been perfected, 

 to condense the air in the buoy by the effect of repeated 

 oscillations, until a valve loaded to a definite pressure would 

 open automatically and allow the air to escape. In this way 

 the sound from the accumulated pressure would be pro- 

 duced at intervals to a greater or less extent, and would 

 serve to diversify the character of the sound so as to enable 

 the mariner to distinguish different locations. The inven- 

 tion — even in its present form, is considered a valuable addi- 

 tion to the aids to navigation, has received the unqualified 

 approbation of all navigators on this coast who are acquainted 

 with its operation, and will probably be introduced in all 

 countries where its merits are known. Experience has shown 



