484 RESEARCHES IN SOUND. 



The intermittent action of fog-signals makes it necessary to employ a peculiar form 

 of boiler. The steam used is at a high pressui-e, and drawn off at intervals ; couso- 

 quently there is a tendency to foam and throw out water with the steam. To obviate 

 this difficulty tiie form of boiler found by experience to be best adapted to this service 

 is a horizontal tubular boiler (locomotive), with rather more than one-half of the inte- 

 rior space allowed for steam-room. The steam-dome is very large, and is surmounted 

 by a steam pipe 12" in diameter. Both the dome and pipe were formerly made much 

 smaller, but were gradually enlarged as long as any difficulty with regard to foaming 

 was noticed. The steam is dra\\Ti off at a point 10" above the water-level in the 

 boiler. The main points to be observed are to have plenty of steam-room, and to draw 

 the steam from a point high above the Avater-level. It will be readily perceived that 

 a vertical tubular boiler is entirely unsuited to this work. 



It is essential, both as regards economy of fuel and the efQcient working of the sig- 

 nal, that the boiler, including the dome and stand-pipe, should be well covered with 

 some good non-conductor of heat. A material, called salamander felting, manufac- 

 tured in Troy, N. Y., was used on the fog- whistle boiler at House Island during the 

 winter of 1870. There resulted a saving of more than 20 per cent, of fuel over that 

 consumed in the same boiler when uncovered. WTiere this material cannot be pro- 

 cured, a thick layer of hair felting, covered with canvas, will be found to answer a 

 good purpose. 



Various expedients have been proposed with the view of keeping the water in the 

 boilers hot when the signals are not in operation, that the signal may always be ready 

 to sound at a very short notice, and that the water in the boiler and pipes may be 

 prevented from freezing in extremely cold weather. One of these contrivances is 

 " Sutton's circulating water-heater." It consists essentially of a small, vertical, tubu- 

 lar boiler, entirely filled with water, and connected with the boiler or tank which 

 contains the water to be heated, by two pipes on different levels. As soon as the 

 water in the heater is warmed, a circulation commences, the hot water flowing through 

 the upper pipe into the boiler, and the cold through the lower pipe from the boiler to 

 the heater. As the furnace in the heater is very small but little fuel is consumed, and 

 nearly the entire heat produced by the combustion is utilized. 



The apparatus has been extensively employed in heating the water in tanks designed 

 £pr filling the steam fire-engine boilers, when the alarm of fire is first given, and ajipears 

 admirably adapted to thispurpose. If used in connection with a steam-boiler, it should 

 be disconnected before steam is raised in the latter, as, from its construction, it is not 

 calculated to withstand any considerable pressure. 



An arrangement, similar in principle, has been used in the first light-house district, 

 consisting of a small cylinder coal-stove, of the ordinary pattern, around the interior 

 of which, and above the grate, is introduced a single coil of f" pipe. This coil is 

 connected with the boiler by two pipes, one entering near the bottom, the other about 

 2 feet higher. It has been found that in consequence of the rapid circulation of the 

 water through this coil, and the great capacity of Avater for heat, that nearly all the 

 heat froTii the tire in the stove is transferred to the water in the boiler. This arrange- 

 ment possesses the advantage of the f " pipe, being strong enough to stand any press- 

 ure that can be used in the boiler, rendering it unnecessary to disconnect it at any time. 



Experience has, however, proved that none of these contrivances are essential. It 

 is seldom that an attentive keeper cannot foresee the approach of fog or snow in time 

 to have the apparatus in operation as soon as required, even when obliged to start his 

 fire with cold water in the boiler. 



Keepers should be directed to watch the state of the weather carefully, and to light 

 their tires at the first indication of fog or snow-storm. As soon as the water in the 

 boiler is near the boiling point, should the necessity for sounding the signal have not 

 yet arisen, the fire may be banked, and in this state the water may be kept hot for any 

 length of time at a moderate expenditure of fuel. With proper care, no more fuel is 

 required to keep the water at the requisite temperature by means of a banked fire than 

 by any other method, and it is a matter of great imj)ortance to avoid complicating 

 fog-signal apparatus by unnecessary appendages. 



The same plan should be adopted in extremely cold weather to prevent the water 

 in the boiler from freezing. There should bo a small air-cock in the draught-pipe near 

 its junction with the feed-pump, and in cold weather this should be opened when the 

 jiump is not in use, in order to allow the pipe to empty itself. 



^Vhen the draught-pipe cannot be protected from the cold, and the well is at a con- 

 siderable distance from the engine, the following expedient has been employed with 

 success : The pipe is inclosed in an India-rubber hose of about double its diameter, 

 and from time to time steam is forced through the space between the hose and draught- 

 pil>e by means of a small pipe from the boiler. 



Altliough the laws governing the reflection of light and heat are undoubtedly, in a 

 great measure, applicable to sound, there are yet so many disturbing influences, such as 

 inflection, refraction, caused by the varying density of the atmosphere, &c., interfering 

 with the reflection of the latter, that but little use can bo made of this property in 



