RESEARCHES IN SOUND. 463 



modification of his invention, in which a hot-air engine of Ericsson's 

 patent was substitnted as the motive power, instead of the horse; and 

 the writer ot this report, as chairman of the committee on experiments 

 in hehalf of the board, examined this invention and reported in favor of 

 its adoption. The other members of the committee made an nnfavorable 

 report, on the ground that fog-signals were of little importance, since the 

 mariner should know his place by the character of his soundings in all 

 places where accurate surveys had been made, or should not venture 

 near the coast until the fog was dissipated. The board however estab- 

 lished DaboU trumpets at different stations, which have been in constant 

 use up to the present time. 



PART I.— INVESTIGATIONS FROM 18C5 TO 1872.* 

 Experiments near New Haven, in 1865. 



The subject of sound, in connection with fog-signals, still continued to 

 occu])y the attention of the board, and a series of investigations was 

 made in October, 18G5, at the light-house near New Haven, under the 

 direction of the writer of this report, in connection with Commodore, now 

 Admiral, Powell, insi)ector, and Mr. Lederle, acting engineer of the third 

 district. 



The principal object was to compare the sound of bells, of steam- 

 Avhistles, and other instruments, and the effect of reflectors, and also the 

 opeiation of different hot-air engines. For this purpose the committee 

 was furnished with two small sailing-vessels. As tbese were very imper- 

 fectly ai)plicable, since they could not be moved without wind, the writer 

 of the report devised an in.strument denominated an "artificial ear," by 

 which the relative penetrating power of different sounding bodies could 

 be determined and expressed in numbers by the removal of the observer 

 to a comparatively short distance from the point of origin of the sound. 

 This instrument consisted of a conical horn, made of ordinary tinned 

 sheet iron, the axis of which was about 4 feet in length, the diameter of 

 the larger end 9 inches, and tapering gradually to 1| of an inch at the 

 smaller end. The axis of this horn was bent at the smaller end in a 

 gentle curve, until the plane of the section of the smaller end was at 

 I'ight angles to the perpendicular section of the larger end, so that when 

 the axis of the trumpet was held horizontally and the larger section 

 vertically, then the section of the smaller end would be horizontal. 

 Across the smaller end a thin membrane of gold beater's shiu was slightly 

 stretched and secured by a thread. On this membrane fine sand was 

 strewn. To protect the latter from disturbance b}^ the wind, it was sur- 

 rounded by a cylinder of glass, cut from a lamp-chimney, the upper end 

 of which was covered with a plate of glass; and, in the improved condi- 



* From the Report of the Light- House Board, for 1874. 



