earned for himself so high a reputation as an aëronaut, 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 carried 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 surpassing 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 intensity 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 experimental 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, 73⁄4 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 Canadian whistle once heard. It was now adjusted to produce its ordinary low-pitched note, which was immediately heard. Still farther
- ↑ 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.
