C. GENERAL PHYSICS. 1S1 



Professor Mayer has in the above manner also shown the 

 reflecting power of cold coal gas, of cold hydrogen, and car- 

 bonic-acid gas. Amer. Jour, of Science , November, 1874. 



OX THE ATMOSPHERE AS A VEHICLE OF SOUND. 



Professor Tyndall, in a paper with the above title, has giv- 

 en to the Royal Society the results of his experiments on the 

 transmission of the sounds of fog-horns and cannon through 



O CI? 



the atmosphere. To show Tyndall's results, and the conclu- 

 sions he arrived at to explain them, we can not do better 

 than quote the following passages from his paper: 



"Thus far the investigation proceeded with hardly a 

 gleam of a principle to connect the inconsistent results. The 

 distance reached by the sound on the 19th of May was 3|- 

 miles; on the 20th it was 5^ miles; and on the 2d of June 

 6 miles; on the 3d more than 9 miles; on the 10th it was 

 also 9 miles; on the 25th it fell to 6-| miles; on the 26th it 

 rose again to more than 9^ miles ; on the 1st of July, as we 

 have just seen, it reached 12f miles, whereas on the 2d the 

 range shrunk to 4 miles. None of the meteorological agents 

 observed could be singled out as the cause of the fluctu- 

 ations. The wind exerts an acknowledged power over sound, 

 but it could not account for these phenomena. On the 25th 

 of June, for example, when the range was only 6^- miles, the 

 wind was favorable ; on the 26th, when the range exceeded 

 9^ miles, it was opposed to the sound. Nor could the vary- 

 ing optical clearness of the atmosphere be invoked as an ex- 

 planation ; for on July 1, when the range was 12f miles, a 

 thick haze hid the white cliffs of the Foreland, while on many 

 other days, when the acoustic range was not half so great, 

 the atmosphere was optically clear. Up to July 3d all re- 

 mained enigmatical ; but on this date observations were 

 made which seemed to me to displace surmise and perplex- 

 ity by the clearer light of physical demonstration. 



"On July 3d we first steamed to a point 2.9 miles south- 

 west by west of the signal-station. No sounds, not even the 

 guns, were heard at this distance. At 2 miles they M'ere 

 equally inaudible. But this being the position in which the 

 sounds, though strong in the axis, invariably subsided, we 

 steamed to the exact bearing from which our observations 

 had been made upon July 1. At 12:15 P.M., and at a dis- 



