112 Mr. Galbraith on the Velocity of Sound. 



Comparing the experiments made in January with those 

 in July, we have 



Bar. Ther. Hygr. Velocity. 



1 30-124 7905 6-20 1101 — -Six 18-8 =- 3-948 



7', 29-914 88-05 27-85 1164 +7-6 x M4=+ 8-664 



+1101-000 



— 0-210, +7-60, +21-65 63 



1105-716 



58-284 „-f ,. , rr< 11- 1, . 1164-000 



Hence = 2-7 feet for one degree of uoldingham s 



21 '65 hygrometer. 5^.284 



Combining two and two in this manner the twelve monthly 

 experiments about thirty different ways most likely to pro- 

 duce correct results, we found 2*87 feet, from a mean of the 

 whole, for one degree of his hygrometer*. 



Introducing the foregoing principles, we may obtain a ge- 

 neral formula for determining the velocity under any given 

 circumstances. 



If we put a for the change of velocity for a variation of one 

 inch of the English barometer, (3 for that of one degree of 

 Fahrenheit's thermometer, and y for that of one degree of 

 Goldingham's hygrometer, V being the true velocity x'equired, 

 and V that under known circumstances ; then, 



V = V + u{^-p) + ^{f- t) + y{h<^ h) (7) 



Now fi'om a mean of all Mr. Goldingham's experiments we 

 have V = 1100 feet at 30 inches, 60° Fahrenheit, and 14° 

 Goldingham's hygrometer. Also a = 18*8 feet, /3 = l-lifoot, 

 y = 2-87 feet, p = iiO inches, t = 60° Fahrenheit, h = 14° 

 hygrometer ; and p', t\ and A', the observed states of the ba- 

 rometer, thermometer, and hygrometer respectively. 



But the velocity of sound is modified a little by the velo- 

 city and direction of the wind. Dr. Gregory observes, " that 

 when the direction of the wind concurs with that of the sound, 

 the sum of their separate velocities gives the apparent velocity 

 of sound ; and when the direction of the wind opposes that of 

 the sound, the difference of the separate velocities must be 

 taken." 



* ft were greatly to be desired that Mr. Goldingham would, if possible, 

 give the means of comparing his hygrometer with some standard, or witli 

 Mr. Daniel's, which seems to have met with considerable approbation for 

 its accuracy- This might perhaps be accomplished in some such manner 

 as Biot has by analysis compared Dc Luc's and Saussurc's. 



We have lieard that Mr. Thomas Jones, of Cockspur-street, has lately in- 

 vented an improved hygrometer which may be useful in these researches. 



Now 



