392 WRITINGS OF JOSEPH HENRY. [1874 



report, in connection with General 0. M. Poe, engineer-secre- 

 tary of the Light-House Board, Commodore (now Admiral) 

 Augustus L. Case, then inspector of the third light-house 

 district, and Mr. Lederle, acting engineer of the same 

 district. 



The principal object of these investigations was to com- 

 pare different instruments and to ascertain the improvements 

 which had been made in them since the date of the last 

 investigations, especially the examination of a new fog-signal 

 called the siren, and the comparison of it with the Daboll 

 trumpet, although other investigations were made relative 

 to the general subject of sound in relation to fog-signals. 

 The locality chosen was Sandy Hook, a narrow peninsula 

 projecting northward about five miles into the middle of the 

 Lower Bay of New York, (and almost at right angles to its 

 coast,) having a width of about half a mile. Near the north- 

 ern point on the east shore a temporary building was erected 

 for the shelter of the engines and other instruments. 



The comparisons in regard to penetrating power were 

 made by the use of the artificial ear heretofore described, by 

 carrying this off a measured distance until the sand ceased 

 to move. This operation was much facilitated by previous 

 surveys by members of the engineer corps, who had staked 

 off a straight line parallel with the shore, and accurately 

 divided it into equal distances of 100 feet. 



On account of the character of the deep and loose sand, 

 walking along this distance was exceedingly difficult, and to 

 obviate this, a carriage with broad wheels drawn by two 

 horses was employed. An awning over this vehicle protected 

 the observer from the sun, and enabled him without fatigue 

 and at his ease to note the agitations of sand on the drum of 

 the artificial ear, the mouth of which was directed from the 

 rear of the carriage toward the sounding instrument. 



For these and other facilities we were indebted to General 

 Andrew A. Humphreys, chief of the Engineer Bureau, who 

 gave orders to the officer in charge of the military works at 

 Sandy Hook to afford us every aid in his power in carrying 

 on the investigation. 



