700 THE POPULAR SCIENCE MONTHLY. 



earned for himself so high a reputation as an aeronaut, and who has 

 always shown himself so willing to promote a scientific object, I 

 learned with regret that the experiment was too dangerous to be car- 

 ried out. 1 



Atmospheric Selection. It has been stated that the atmosphere 

 on different days shows preferences to different sounds. This point is 

 worthy of further illustration. 



After the violent shower which passed over us on October 18th, 

 the sounds of all the instruments, as already stated, rose in power ; 

 but it was noticed that the horn-sound, which was of lower pitch than 

 that of the siren, improved most, at times not only equaling but sur- 

 passing the sound of its rival. From this it might be inferred that 

 the atmospheric change produced by the rain favored more especially 

 the transmission of the longer sonorous waves. 



But our programme enabled us to go further than mere inference. 

 It had been arranged on the day mentioned, that up to 3.30 p. m. the 

 siren should perform 2,400 revolutions a minute, generating 480 waves 

 a second. As long as this rate continued, the horn, alter the shower, 

 had the advantage. The rate of rotation was then changed to 2,000 

 a minute, or 400 waves a second, when the siren-sound immediately 

 surpassed that of the horn. A clear connection was thus established 

 between aerial reflection and the length of the sonorous waves. 



The 10-inch Canadian whistle being capable of adjustment so as to 

 produce sounds of different pitch, on the 10th of October I ran through 

 a series of its sounds. The shrillest appeared to possess great inten- 

 sity and penetrative power. The belief is common that a note of this 

 character (which affects so powerfully, and even painfully, an observer 

 close at hand) has also the greatest range. Mr. A. Gordon, in his 

 examination before the Committee on Light-houses, in 1854, expressed 

 himself thus: "When you get a shrill sound, high in the scale, that 

 sound is carried much farther than a lower note in the scale." I have 

 heard the same opinion expressed by other scientific men. 



On the 14th of October the point was submitted to an experi- 

 mental test. It had been arranged that up to 11.30 a. m. the Canadian 

 whistle, which had been heard with such piercing intensity on the 

 10th, should sound its shrill note. At the hour just mentioned we 

 were beside the Varne buoy, Vf miles from the Foreland. The siren, 

 as we approached the buoy, was heard through the paddle-noises ; 

 the horns were also heard, but more feebly than the siren. "We paused 

 at the buoy and listened for the 11.30 gun. Its boom was heard by 

 all. Neither before nor during the pause was the shrill-sounding Ca- 

 nadian whistle once heard. It was now adjusted to produce its ordi- 

 nary low-pitched note, which was immediately heard. Still farther 



1 Experiments so important as those of De la Roche ought not to be left without 

 verification. I have made arrangements with a view to this object. 



