400 WRITINGS OF JOSEPH HENRY. [1874 



and whistle should be in unison, but it may be doubted 

 whether an increase of effect, with a given amount of power, 

 would result from using such an arrangement; it might nev- 

 ertheless be of advantage in certain cases to direct the sound 

 of a locomotive whistle in a definite direction, and to use a 

 smaller whistle, especially in cities in which the locomotive 

 passes through long streets ; perhaps in this case the sound 

 might be less disagreeable than that of the naked whistle, 

 which sends its sound-waves laterally with as much force as 

 in the direction of the motion of the engine. 



6. General Poe called attention to the sound produced by 

 the paddle-wheels of a steamer in the offing — at a distance 

 estimated at four and a half miles. The sound was quite 

 distinct when the ears were brought near the surface of the 

 beach. 



In this connection he stated that he had heard the ap- 

 proach of a small steamer on the northern lakes when its 

 hull was still below the horizon, and was even enabled to 

 designate the particular vessel from among others by the 

 peculiarity of the sound. 



The sound in the case of the steamer is made at the sur- 

 face of the water, and it might be worth the trouble to try 

 experiments as to the transmission of sound under this con- 

 dition, and the collection of it by means of ear-trumpets, the 

 mouths of which are near the water, the sound being con- 

 veyed through tubes to the ears of the pilot. In order how- 

 ever to determine in this case the direction of the source of 

 sound, two trumpets would be necessary, one connected with 

 each ear, since we judge of the direction of a sound by its 

 simultaneous effects on the two auditory nerves. This sug- 

 gestion, as well as many others which have occurred in the 

 course of these researches, is worthy of special investigation. 



7. A series of experiments was made to compare trumpets 

 of different materials and forms, having the same length and 

 transverse areas, all blown at a pressure of 9J pounds. 



