DISCOURSE OF W. B. TAYLOR. 311 



wide, and half an inch thick at its smaller vibrating end, and was 

 blown by a hot-air engine ; and lastly a large siren horn operated 

 by steam at different pressures, the aerial vibration being produced 

 by the intermittence of a revolving grating disk or valve in the 

 small end of the horn, driven at high velocities by the steam 

 engine, and its pitch regulated by the adjustable speed of the revolv- 

 ing disk. The trumpet or fog-horn was provided with a series of 

 replaceable steel tongues of different sizes, and the siren was driven 

 at five different pitches of from 250 to 700 impulses per second, 

 and at steam pressures varying from 20 pounds to 100 pounds per 

 square inch. For the purpose of accurate estimation, within short 

 distances, a phonometer or " artificial ear " was employed, having 

 at its smaller upturned end a horizontal drum of stretched mem- 

 brane, sprinkled with sand, after the plan devised by Sondhauss. 

 Trumpets of the same size, were made of different materials, as of 

 brass, iron, and wood; but these differences were found to exercise 

 little or no influence on the intensity or penetration of the sound. 

 Trumpets were also made of different shapes, straight and curved, 

 and square as well as round, with equal lengths and equal areas of 

 cross section; from whose trials it appeared that the conical form 

 gave nearly double the distance of action on the sand of the "arti- 

 ficial ear," that was given by the pyramidal form. Such investi- 

 gations varied and long-continued, serve to show the conscientious 

 earnestness with which Henry sought to give the highest efficiency 

 to the expedients available for the protection of life and property 

 along our extended sea coast. 



The steam-whistle was found to be less powerful than the trum- 

 pet, with the same expenditures of fuel. Steam- whistles were 

 afterwards tried of 10 inches, 12 inches, and 18 inches in diameter. 

 The largest size was not found to give results proportioned to its 

 increased consumption; and the 10 or 12 inch size was regarded 

 as practically the most efficient. The siren was found to be the 

 most powerful and penetrating of the instruments tested, as it 

 admitted more advantageously the application of a higher steam 

 expenditure. The best result with this instrument was attained 

 with a pressure of from 60 to 80 pounds, and at a pitch between 

 350 and 400 vibrations per second. Under favorable conditions, 



