482 EESEARCHES IN SOUND. 



[This statement is in a measure in accordance uith results wliicli I 

 have previously found in connection with investigations at the light- 

 house near l^ew Haven, in which the conclusion was arrived at, that 

 although rays of feeble sounds, and for a short distance, observe the 

 law that the angle of reflection is equal to the angle of incidence after 

 the manner of light, yet powerful sounds tend to diverge laterally to 

 such a degree as to render reflectors of comi^aratively little use.] 



In view of these circumstances, it will be obvious that it was extremely difficult to 

 determine the extent of the power of the various signals under examination. 



It should be remembered that while the sound from the whistle is equally distrib- 

 uted in all directions,* that from the two other signals, both of which arc i^rovided 

 with trmupets, is not so distributed. 



[The difference is apparent near by, but, as we have seen before, on 

 account of the tendency of sound to spread it is imperceptible at a dis- 

 tance.] 



In the siren the sound is most distinct in the axis of the trumpet. 



In the Daboll trumpet it is usually strongest in a x^lane i^erx^endicular to this axis. 



[This is at variance directly with any observation I have myself made.] 



Relative poiver. — From the average of a great number of experiments the following 

 result was obtained : 



The power of the first-class siren, 12" whistle, and first-class Daboll trumpet, may 

 be expressed by the numbers 9, 7, 4. 



The extreme limit of sound of the siren was not ascertained. That of the 12" whistle 

 is about twenty miles, and of the trumpet twelve. 



Consnmjytion of fuel and ivatcr. — The siren, when working with a pressure of 72 pounds 

 of steam, consumes about 180 pounds of coal and 126 gallons of water per hour. 



The 12" whistle, with 55 pounds pressure of steam, consumes 60 pounds of coal and 

 40 gallons of water per hour. 



The Daboll trumpet, with 10 pounds pressure of air in the tank, consumes about 20 

 pounds of coal iier hour. 



The relative expenditure of fuel would be : siren, 9 ; whistle, 3 ; trumpet, 1. 



The siren. — Of the three machines this is the most complicated. It uses steam at a 

 high pressure, and some of its parts move with very great velocity, the siren spindle 

 making from 1,800 to 2,400 revolutions per minute. The boiler nuist be driven to its 

 full capacity in order to furnish sufficient steam. A large quantity of steam is, ab 

 intervals, suddenly drawn from the boiler, causing a tendency to foam, and to eject a 

 considerable amount of water through the trumpet. 



The constant attention of the keeper is required to regulate the fire, the supply of 

 water to the boiler, of oil to the journals, &c. 



In general terms, it may be stated that the siren requires more skill and attention 

 in its management than either of the other signals. 



The Daboll trumpet. — As the caloric engine, which has been hitherto employed to 

 ojierate this signal, requires little fuel, no water, and is jierfectly safe as regards 

 danger from explosion, it would, at the first glance, appear to be the most suitable 

 power that could be applied to fog-signals, and was accordingly at first exclusively 

 jwlopted for this jiurpose. It was however found to be so liable to accident and so 

 difficult to repair that of late years it has been almost entirely rejected. In the steam- 

 boiler the furnace is surrounded by water, and it is impossible, under ordinary circum- 

 stances, to heat the metal much above the temperature of the water. The furnace of 

 the caloric engine is surrounded by air, and is therefore liable to be burned out if the 

 tire is not properly regulated. 



The working-piston is packed with leather, and as it moves horizontally, with its 

 whole weight resting on the lower side of the cylinder, the packing at its lower edge 

 is soon worn out. 



If the engine is allowed to stop with the piston at the furnace-end of the cylinder, 



* The sound of the whistle is equally distributed horizontally. It is, however, 

 much stronger in the plane containing the lower edge of the bell than on either side 

 of this plane. Thus, if the whistle is standing upright, in the ordinary position, its 

 soviud is more distinct in a horizontal plane i)assiug through the whistle than above 

 or below it. 



