1874] WRITINGS OF JOSEPH HENRY. 393 



The instruments emplo3'ed were — 



1st. A first-class DaboU trumpet (the patent for which, 

 since the death of Mr. Daboll, is owned by Mr. James A. 

 Robinson,) operated by an Ericsson hot-air engine. It car- 

 ried a steel reed 10 inches long, 2| inches wide, and ^ inch 

 in thickness at the vibrating end, but increasing gradually 

 to an inch at the larger extremity. This was attached to a 

 large vertical trumpet curved at the upper end into a hori- 

 zontal direction and furnished with an automatic arrange- 

 ment for producing an oscillation of the instrument of about 

 60° in the arc of the horizon. Its entire length, including 

 the curvature, was 17 feet. It was 3^ inches at the smaller 

 end and had a flaring mouth 38 inches in diameter. The 

 engine had a cylinder 32 inches in diameter, with an air- 

 chamber of 4| feet in diameter and 6 feet long, and was able 

 to furnish continually a five-second blast every minute at a 

 pressure of from 15 to 30 pounds. 



2d. A siren, originally invented by Cagniard de Latour, 

 and well known to the physicist as a means of comparing 

 sounds, and measuring the number of vibrations in different 

 musical notes. Under the direction of the Light-House 

 Board, Mr. Brown, of New York, had made a series of experi- 

 ments on this instrument in reference to its adoption as a 

 fog-signal, and these experiments have been eminentl}'^ suc- 

 cessful The instrument as it now exists differs in two essen- 

 tial particulars from the original invention of Latour: 1st, 

 it is connected with a trumpet in which it supplies the place 

 of the reed in producing the agitation of the air necessary to 

 the generation of the sound ; and 2d, the revolving disk, 

 which opens and shuts the orifices producing the blasts, is 

 driven not by the blast itself impinging on oblique openings, 

 as in the original instrument, but by a small engine con- 

 nected with the feed-pump of the boiler. 



The general character of the instrument ma}^ be under- 

 stood from the following description : Suppose a drum of 

 short axis, into one head of which is inserted a steam-pipe 

 connected with a locomotive boiler, while the other end 

 has in it a triangular orifice through which the steam is at 



