1874] WRITINGS OF JOSEPH HENRY. 405 



appear to be reflected after the manner of light and heat, but to roll aloni^ 

 it like a cloud of smoke. 



This statement is in a measure in accordance with results 

 which I have previously found in connection with investi- 

 gations at the light-house near New Haven, in which the 

 conclusion was arrived at, that although rays of feeble sound 

 for a short distance observe the law that the angle of re- 

 flection is equal to the angle of incidence — after the manner 

 of light, yet those of powerful sound tend to diverge laterally 

 to such a degree as to render reflectors of comparatively 

 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 

 distributed in all directions,* that from the two other signals, both of which 

 are provided with trumpets, is not so distributed. 



The diffierence is apparent near by, but (as we have seen 

 before) on account of the tendency of sound to spread, it is 

 imperceptible at a distance. 



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

 In the DaboU trumpet it is usually strongest in a plane perpendicular to 

 this axis. 



This is at variance directly with any observation I have 

 myself made. 



Relative power. — From the average of a great number of experiments the 

 following result was obtained : 



The power of the first-class siren, 12-inch 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-inch whistle is about twenty miles, and of the trumpet twelve. 



Consumption of fuel and water. — 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-in. 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 per hour. 



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



*The sound of the whistle is equally distributed horizontally. It is how- 

 ever 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 sound is more distinct in a horizontal plane passing 

 through the whistle, than above or below it. 



