472 EESEARCHES IN SOUND. 



ing him toward a liglit-vessel, tlie locality of which he expected to find 

 by means of the fog-signal. He kept on his course until he thought 

 himself very near the ship, without hearing the stroke of the bell. He 

 then anchored for the night, and found himself next morning within a 

 short distance of the light- vessel, but still heard no sound, although he 

 was assured when he got to it that the bell had been ringing all night. 

 He then passed on in the same direction in which he had previously 

 sailed, leaving the light-vessel behind, and constantly' heard the bell for 

 a distance of several miles, the density of the fog not perceptibly dimin- 

 ishing. In this case it is evident that the deadening of the sound was 

 not due to the fog, but, as we shall hereafter see, in all i:)robability to the 

 combined action of the upper and the lower currents of air. 



On returning to Washington the writer took advantage of the occur- 

 rence of a fog to make an exi^eriment as to the penetration of the sound 

 of a small bell rung by clock-work, the apparatus being the part of a 

 moderator-lamp intended to give warning to the keepers when the sup- 

 ply of oil ceased. The result of the experiment was contrary to the sup- 

 position of absorption of the sound by the fog, but the change in the 

 condition of the atmosi)here as to temperature and the motion of the 

 air, before the experiment could be repeated in clear weather, rendered 

 the result not entirely satisfactory. 



Experiments at Sandy Hook in 18C7. 



The next series of experiments was made from October 10 to October 

 18, 18G7, under the direction of the wrirer of this report, in connection 

 with General Poe, engineer-secretary of the Light-House Board, Com- 

 modore (now Admiral) Case, then inspector of the third light-house dis- 

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



The principal object of these investigations was to compare different 

 instruments, and to ascertain the improvements which had been made 

 in them since the date of the last investigations, especially the exami- 

 nation of a new fog-signal called the siren, and the comparison of it with 

 the DaboU 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 JS^ew York, and al- 

 most at right angles to its coast, having a width of about lialf a mile. 

 Near the northern 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 

 ineasured distance until the sand ceased to move. This operation was 

 much facilitated by previous surveys of 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 deei) and loose sand, walking 



