386 WRITINGS OF JOSEPH HENRY. [1874 



and its use has consequently been abandoned ; another hot- 

 air engine has been employed by the board, the invention 

 of a Mr. Wilcox, which has also been discontinued for a 

 similar reason. I was assured by the person last named, a 

 very ingenious mechanician, that when the several patents 

 for hot-air engines expired, a much more efficient instrument 

 could be devised by combining the best features of each of 

 those now in use. 



For determining the relative penetrating power of these 

 instruments, the use of two vessels had been obtained, with 

 the idea of observing the sound simultaneously in opposite 

 directions. 



Unfortunately however, the location which had been chosen 

 for these experiments was of a very unfavorable character in 

 regard to the employment of sailing-vessels and the use of 

 the artificial ear. It was fully open to the ocean only in a 

 southerly direction, navigation up the bay to the north being 

 limited to three and a half miles, while on shore a sufficient 

 unobstructed space could not be obtained for the proper use 

 of the artificial ear. With these obstructions and the neces- 

 sity of beating against the wind, thereby constantly altering 

 the direction of the vessel, exact comparisons were not pos- 

 sible, yet the observations made were sufficiently definite to 

 warrant certain conclusions from them as to the relative 

 power of the various instruments submitted to examination. 



The following is a synopsis of the observations on four 

 different days. Before giving these, it is necessary to ob- 

 serve that at each stroke of the piston of the hot-air engine 

 a loud sound was produced by the blowing off of the hot 

 air from the cylinder, after it has done its work. In the 

 following statement of results the noise thus produced is 

 called the exhaust. On the first day, but one set of observa- 

 tions was made, the vessel's course being nearly in the line 

 of the axis of the trumpet. The order of penetrating power 

 was as follows : 1st, trumpet ; 2nd, exhaust ; 3d, bell ; these 

 instruments being heard respectively at 5^, 3^, and 2 miles. 

 The whistle was not sounded. 



On the second day, simultaneous observations were made 



