1874] WRITINGS OF JOSEPH HENRY. 411 



The 10-in. and 12-in. whistles are recommended for ordinary use. The 18-in. 

 whistle is more powerful, but the increase of power bears too small a propor- 

 tion to that of the expenditure of fuel to render its employment generally 

 advisable. The best results were obtained by giving the whistle the follow- 

 ing proportions : The diameter of the bell equaling two-thirds of its length, 

 and the set of the bell, i. e., the vertical distance of the lower edge above the 

 cup, the one-third to one-fourth of the diameter for a pressure of 50 to 60 

 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 cannot 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 provided with bells, as there 

 are occasions when they may serve a useful purpose, but it should be well 

 understood by mariners that they must not expect always to hear the bells 

 as a matter of course. 



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

 especially when 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 farther 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 machiner}^ is so slight as to be inappreciable ex- 

 cept at a short distance. 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 per- 

 manently placed with the axis of its mouth directed horizon- 

 tally, and in this position, if the bell were struck interiorly 

 with a hammer, which would give it a larger vibration than 

 if struck exteriorly, I doubt whether any difference would 

 be observed between the two methods of ringing ; and if any 

 existed it would probably be in favor 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 arrangement of the machinery the intervals between the 

 strokes of the bell may be so regulated as to avoid the danger of confound- 

 ing the signals, however near together. 



Although a bell may be heard better when sounded by hand than by clock- 

 work, yet in thoroughfares where the signal must be kept in constant opera- 

 tion during the entire continuance of a fog, it would be impracticable to 

 make use of the former method, and recourse must be had to machinery. 



