688 ATMOSPHERIC REFRACTION AT LOW TEMPERATURES, 



Expansion of Air, p. 245. 



A glass cylinder, 1'7 inch in diameter and 2*6 inches in length, 

 was used ; into this was fitted a long tube or stem 10 inches in 

 length and nearly half an inch in diameter, graduated into 140 

 equal parts. The cylinder was also fitted with a ground glass 

 stopper. A drop of mercury was placed in the stem, and the 

 vessel carried from a cold atmosphere to a warm one, and then 

 the temperature taken by removing the stopper. Again, the 

 vessel was carried from the warm room to the cold, and the 

 results showed that 2059*854 volumes of air at 55° '6 F. are re- 

 duced to 1682-24 volumes at 34° '5 F. 



9. Experiments and Observations on Sound. (Parry's First 

 Voyage, &c.) 



The distance at which sounds w^ere heard during intense cold 

 constantly afforded matter for surprise. 



" We have often heard people distinctly conversing in a com- 

 " mon tone of voice at the distance of a mile." A man was heard 

 singing to himself as he walked along the beach at even a greater 

 distance than this. 



[These facts, recorded by Parry, are no doubt due to the singu- 

 larly homogeneous nature of the air over the whole region. 



The experiments of Prof. Tyndall in the English Channel show 

 that whether the weather be foggy or clear, the air will convey 

 sound well, provided it is homogeneous ; but that if there are 

 layers of air of different densities, or if there are dry and moist 

 currents of air alternating, then the sound will be reflected or 

 diffused at the common surface of two layers, and will be lost. 

 The acoustic transparency of the air and its optical transparency 

 are entirely independent of one another.] 



10. The Velocity of Sound. (Franklin's Second Journey.) 



Observations on the velocity of sound at different temperatures 

 were made by Lieutenant E. N. Kendall during October, Novem- 

 ber, and December 1825. 



The experiments, divided into five series, according to the 

 temperatures at the time of observation, give the following 

 results : — 



Temperature. Velocity of Sound. 



28-0 to 



27-0 F. - 



- 1112 feet per second. 



10-0 to 



3-0 



- 1089 



2-0 to 



- 4-0 - 



- 1079 



36-0 to 



-35-5 - 



- 1036- 1 



41-0 



- 



- 1030-3 „ 



