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XIV. On the Velocity of Sound. l?j/ Wm.Galbuaith, jEJsy. 



To the Editor of the Philosophical Magazine and Journal, 

 Sir, 

 CHOULD the accompanying analysis of some of the late 

 ^ experiments on the velocity of sound meet with your ap- 

 probation, you will oblige me by giving it a place in your 

 Journal. I am, yours &c. 



Edinburgh, July 12, 1825. Wm. Galbraith. 



The velocity of sound transmitted through the atmosphere 

 has lately attracted some attention. The results deduced from 

 experiments presented several discrepancies which it was de- 

 sirable to remove. This could only be accomplished by new 

 and varied series of experiments, under a variety of circum- 

 stances and in different climates. Among the early investi- 

 gators of this problem, the eifect of barometric pressure, tem- 

 perature, and moisture was not sufficiently attended to, and 

 consequently their theoretical conclusions could only be con- 

 sidered as rude approximations. 



Newton attempted an investigation, in the scholium attached 

 to the fiftieth Proposition of the second book of the Principia^ 

 and by several considerations relative to the nature and con- 

 stitution of the atmosphere, arrived at the conclusion of Der- 

 ham ; namely, that sound moved at the rate of 11 42 feet in 

 a second of time. He immediately adds, however, that 

 " these things will be found true in spring and autumn, when 

 the air is rarefied by the gentle warmth of those seasons, and 

 by that means its elastic force becomes more intense. But in 

 winter, when the air is condensed by the cold, and its elastic 

 force is somewhat remitted, the motion of sound will be slower 

 in the subduplicate ratio of the density; and on the contrary, 

 swifter in sunnner." Now though he did not make any esti- 

 mate of the allowance for the actual state of the atmosphere, 

 it is clear he thought it necessary; and would, without doubt, 

 have determined it, had he been possessed of sufficient data. 



As it was conceived that temperature had a considerable 

 effect in modifying the velocity of sound, an allowance was 

 accordingly made on that account. 



Dalton first proved that the expansions of all aeriform 

 fluids, when insulated from liquids, are uniform by the same 

 increase of temperature, which was verified by Gay-Lussac 

 with a more refined apparatus. They showed that 1*000 in 

 vohmie at 32'^ Fahrenheit, became 1-375 at 212^ Fahrenheit. 

 Hence die increment oi bulk for each degree is 0'375 -^180 = 



0002083 



