EESEAKCHES IN SOUND. 483 



the leather is flestroyed by the heat. The repacking of a piston is a difficult and 

 expensive operation, requiring more skill than can be expected among the class of 

 men from whom light-house keepers are appointed. 



Another accident to which these engines are sulyect arises from a sudden check in 

 the velocity of the piston, caused cither by the jamming of the leather packing or the 

 introduction of dirt into the open en<l of the cylinder, in which case the momentum of 

 the heavj', eccentrically-loaded lly- wheel is almost sure to break the main rocker-shalt. 



The expense of rejiairs is considerably increased by the fact that these engines are 

 not now in general use, and when imjiortant rejjairs are required it is usually neces- 

 sary t o send to the manufacturer. 



This signal requires much attention. The fires must be carefully regulated to avoid 

 burning out the furnace, the journals thoroughly oiled, and the cylinders well sup- 

 plied with tallow. 



The steam-whistle. — This machine requiring much less steam than the siren in propor- 

 tion to the size of its boiler, there is not the same necessity for forcing the fire ; the 

 pressure of steam required is less, and the point trom which it is drawn much higher 

 above the water-level in the boiler, and there is consequently no tendency to foam. 



The machinery is simple ; the ])iston pressiu'e very light, producing but little strain 

 on the different parts of the engine, which is therefore not liable to get out of order 

 and requires no more attention than a common stationary engine. 



One marked advantage possessed by this signal is that should the engine become 

 disabled, the whistle may still be sounded by working the valve by hand. This is not 

 the case with the two others, where an accident to any part of the machinery renders 

 the signal for the time useless. 



It will thus be seen that the siren is the most expensive of the fog-signals as regards 

 maintenance, and that it is adapted only to such stations as are abundantly snpplied 

 with water and situated in the vicinity of machine-shops where the necessary rei>airs 

 can be promptly made. 



On the other hand, as it is the most powerful signal, there are certain stations where 

 it should have the preference ; as, for example, Sandy Hook, which from its import- 

 ance demands the best signal that can be procured, regardless of cost. Such stations 

 should be provided Avith duplicate apparatus, well supx^lied with spare parts, to guard 

 against any possibility of accident. 



There should be a keeper whose sole business must be to attend the signal, and who 

 should have sufficient mechanical skill to make the ordinary repairs. He should 

 moreover be a licensed engineer. 



There will also be required an assistant, who may be one of the light-keepers, to 

 relieve him during the continuance of foggy weather. 



The steam-whistle is the simplest in construction, most easily managed and kept in 

 repair, and requires the least attention of all the fog-signals. It is sufficiently power- 

 ful for most localities, while its consumption of fuel and water is moderate. 



It has been found on this coast that a sufficient quantity of rain-water can be col- 

 lected to supply the 12" whistle at nearly every station. This has been the case for 

 the last two years at Martinicus. 



The Daboll trumpet, operated by a caloric engine, should only be employed in ex- 

 ceptional cases, such as a,t stations where no water can be procured, and where, from 

 the proximity of other signals, it may be necessary to vary the nature of the sound. 



The trumpet however may undoubtedly be very much improved by employing 

 steam power for condensing the air. The amount of work required, which is that of 

 compressing 70 cubic feet of air to an average pressure of 8 jjouuds per inch, would be 

 less than two-horse power. For this ptirpose the expenditure of fuel and water would 

 be moderate ; indeed, the exhaust steam could be condensed and returned to the cis- 

 tern, should the supply of water be limited. 



The sii'en also is susceptible of improvement, especially as regards simplification. 



[In the foregoing remarks we tliink the general has expressed a some- 

 what undue partiality for the whistle, and somewhat overestimated the 

 defects of the other instruments. The trumpets, with Ericsson engine, 

 have not been abandoned, except partially in the two districts under 

 the direction of General Duane, to which he probably intended to con- 

 fine his statement. They are still in use in the third district, where 

 they are preferred by General Woodruff, who finds no difficulty in ];eep- 

 ing them in repair, having employed a skilled machinist who has made 

 these instruments his special study, and who, visiting them from time 

 to time, makes reimirs and supj)lies new parts.] 



