468 RESEARCHES IN SOUND. 



It is a matter of much importance to obtain a liot-air engine of suffi- 

 cient power, and suitable for working fog-signals of all classes. This 

 will be evident when we consider the difficulty in many cases of obtain- 

 ing fresh water for producing steam, and the expense of the renewal of 

 the boilers in the use of salt-water, as well as that of the loss of power 

 in frequently blowing out the latter, in addition to the danger of the use 

 of steam by unskillful attendants. 



The merits of the two engines however under consideration could not 

 be fnlly tested by the short trial to which they were subjected during 

 these experiments. The principal objection to the Ericsson engine was 

 the size of the fly-wheel and the weight of the several parts of the ma- 

 chine ; the Koper engine was much more compact, and api)eared to work 

 with more facility, but from the greater heat imparted to the air the 

 packing was liable to burn out and required to be frequently renewed. 

 Although at first the impression of the committee was in favor of the 

 lioper engine, yet in subsequent trials of actual practice it was found 

 too difficult to be kept in order to be employed for light-house purposes, 

 and its use has consequently been abandoned ; another hot-air engine 

 has been emjiloyed 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 iji regard to the em- 

 ])loyment 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 necessity of beat- 

 ing against the wind, thereby constantly altering the direction of the 

 vessel, exact comparisons were not possible, 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 however, it is necessary to observe tliat at each 

 stroke of the piston of the hot-au' engine a loud sound was produced by 

 jthe 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 observations was made, the 

 vessel's course being nearly in the line of the axis of the trumpet. The 



