-* Mechanical Science » 2Vt 



theory, and such is also the fact, as appears from the following^ 

 decisive observation, for which science is indebted to the Rev. 

 George Fisher, the astronomer in Capt. Parry's Northern Expedi- 

 tions. I shall give it in his own words*. " The experiments on 

 the 9th February, 1822, were attended with a singular circum- 

 stance, which was — the officer's word of command * fire ' was 

 several times distinctly heard both by Capt. Parry and myself, about 

 one beat of the chronometer (nearly half a second) after the report 

 of the gun ; from which it would appear that the velocity of sound 

 depended, in some measure, upon its intensity. The word ' fire * 

 was never heard during any of the other experiments. Upon this 

 occasion the night was calm and clear, the thermometer 25° below 

 zero, the barometer 28.84 inches, which was lower than it had ever 

 been ohsei-ved before at Winter Island." 



This last circumstance was probably not accidental ; and if it is 

 possible in our climate to distinguish the velocity of the sound of a 

 bell from that of a cannon, it is at a time of diminished elasticity 

 of the atmosphere, indicated by a low state of the barometer, that 

 the attempt is most likely to succeed. — H. F. T. 



3. Distances at which Sounds are heard. — " I recollect being, 

 many years ago, at the west end of Dumferline, and hearing part of 

 a sermon then delivering at a tent at Cairninghill. I did not miss 

 a word, although the distance must be something about two miles. 

 It was the late Dr. Black, of Dumferline, who preached, and who 

 perhaps has seldom been surpassed for distinct speaking and a clear 

 voice. The sound was such as I should have expected in favour- 

 able circumstances at a quarter of a mile. The wind, which was 

 steady, but moderate, came in the direction of the sound. I was 

 riding westward, and at length saw the Doctor finishing his sermon^ 

 otherwise I should have doubted whether he had been at such a 

 distance. Whether the sound had run along the road as in a tube, 

 I cannot say. I recollect little of what sort of road it is ; part I 

 think has pretty good dykes which might guide and confine the 

 sound, aided by the wind." — Jameson's Journal, 1827, p. 184. 



4. On the effect of Wind upon Sound. — Amongst other observa- 

 tions upon this point, Mr. Meikle says, " It is generally supposed 

 that the relative velocity of sound and wind is not affected by the 

 motion of the latter ; but this opinion stands much in need of con- 

 firmation. It is clear that the effect of wind on sound is very dif- 

 ferent from merely bearing it along as a current in the ocean does 

 a floating body. For, in this way, the intensity would undergo no 

 sensible change, whereas we know that, in most cases, wind anni- 

 hilates sound when opposed to it, and magnifies it prodigiously 

 when moving in the same direction. The most natural inference 

 which we can draw from this, is, that wind reflects sound in the 



♦ Appendix to Parry's Second Voyage, page 239. 



