486 RESEARCHES IN SOUND. 



[This result, that the pitch varies with the length of the bell, is in 

 conformity with well-established principles of resounding cavities; and 

 that the power should increase with the extent of the aerial reed, the 

 vibrations of which give motion to the resounding air within the cavity, 

 is also, as we have seen, in accordance with hypothetical considerations; 

 but as the density of this stream of steam, and consequently the rapid- 

 ity of its vibrations, depends upon the pressure of the steam in the 

 boiler, a perfect whistle should have the capabiUty of changing its di- 

 mensions, not only in relation to the width of its throat, but also in 

 regard to the pressure of the steam in the reservoir.] 



The j)itch giving the greatest raage appears to be at the middle of the scale of sound. 

 It is certain that a good result cannot be obtained from either a very shrill or a bass 

 note. This remark is applicable to all varieties of signal. 



The 10" and 12" whistles are recommended for ordinary nse. The 18" whistle is 

 more powerful, but the increase of power bears too small a proportion to that of the 

 expenditure of fuel to render its employment generally advisable. The best results 

 were obtained by giving the whistle the following proportions : The diameter of the 

 bell equaling two-thirds of its length, and the set of the bell, i. e., the vertical dis- 

 tance of the lower edge above the cup, the one-thii-d to one-fourth of the diameter for 

 a pressure of 50 to GO pounds of steam 



A bell, whether operated by hand or by machinery, cannot be considered an efficient 

 fog-signal on the sea-coast. In calm weather it caunot be heard half the time at a 

 greater distance than one mile, while in rough weather the noise of the surf will 

 drown its sound to seaward altogether. 



On approaching a station I have frequently seen the bell rung violently by the 

 keeper, without being able to hear the sound until I had landed. 



Nevertheless, all important stations should be ])rovided with bells, as there are occa- 

 sions when they may serve a useful purpose, but it should be well understood by mari- 

 nei'sthat they must not expect always to hear the Ixdls as a matter of course. 



Bells should not be omitted at stations furnished with steam fog-signals, especially 

 wheu the latter are not in duplicate, and mariners should be warned that the bell will 

 be sounded when the regular signal is disabled. 



It has been observed that a bell rung by hand can be heard further than when 

 sounded by machinery, and many of the steamboat companies on this coast pay the 

 keepers of bells rung by clock-work to ring them by hand when the boats of their 

 line are expected to pass. * 



[We think the difference in the effect of ringing of bells by hand or 

 by machinery is so slight as to be inapi^reciable except at a short dis- 

 tance. It is true, as I have before observed, that the sound is louder 

 when the mouth of the bell is directed toward the hearer than when the 

 edge is so directed, but on account of the spreading of this sound the 

 effect is lost in a small distance, and indeed in one light-house the bell 

 is permanently placed with the axis of its mouth directed horizontally, 

 and in this position, if the bell were struck interiorly with a hammer, 

 which would give it a larger vibration than when struck exteriorly, I 

 doubt whether any difference would be observed between the two meth- 

 ods of ringing ; and if any existed it would probably be in fiivor of the 

 fixed bell rung by machinery.] * 



On rivers, narrow channels, and lakes, where the difficulty from the noise of the surf 

 does not exist, this species of signal may be used to advantage, as its maintenance 

 requires but a small expenditure of either money or labor, and by a proper arrange- 

 ment of the machinery the intervals between the strokes of the bell may be so regu- 

 lated as to avoid the danger of confounding the signals, however near together. 



Althotigh a bell may be lieard better when sounded by hand than by clock-work, yet 

 in thoroughfares where the signal must be kept in constant operation during the en- 

 tire continuance of a fog, it would be impracticable to make use of the former method, 

 and recourse must be had to machinery. 



