178 Mr. J. Farey on the Velocity of Sound; 



have been derived lead us to expect that no considerable un- 

 certainty remains with regard to the quantity of this element, 

 which affects all determinations ; for the following calculations 

 I shall adopt + l"-ll sin (tt-fi 33') + 0"-26 cos (u+l° 33'); 

 and from this formula the above given corrections of the single 

 sets of observations have been deduced. 

 [To be continued.] 



XXIX. On the Velocity of Sound; and on the Encke Planet. 

 By Mr. John Farey. 

 To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 

 f HAVE felt much gratified by the perusal of Dr. Gre- 

 gory's late Experiments on the Velocity of Sound in 

 p. 401 of your last volume ; his practical Rule derived from 

 which, may I think prove of great use on many occasions ; and 

 in the mean time, until the Doctor's leisure will enable him 

 to complete his proposed series of Experiments, I beg to pre- 

 sent his practical Rule for calculating the Velocity of Sound, 

 in a somewhat simpler form than it is delivered in p. 411, and 

 to show its agreement with the mean results of all his Ex- 

 periments ; one of which, at 59° of temperature, viz. 1111 feet 

 (not 1113 as printed in p. 407), and another at 66°, viz. \\\5\ 

 feet, have I find been omitted to be brought forwards, and in- 

 cluded in the average velocities in his Table, but which now 

 I have supplied. 



Rule. — To the constant number 1082-7, add half the num- 

 ber of degrees of Fahrenheit's scale, at the time of ob- 

 serving any distant Sound, the sum will be the velocity in 

 feet, of its transmission through the air, in the climate of 

 London. 



According 



