46 Dr. Schroder van der Kolk on the Velocity of Sound. 



0-00925307 on the 27th of June, 

 and 



0-00840467 „ 28th 



If we take for the density of aqueous vapour Gay-Lussac's 

 value, namely five-eighths of that of the air, which nearly agrees 



wes 



with Regnault's determination, the formula s Q =s a / _ZJLl g 



for the two determinations 



339-57 and 338-55, 

 which we have still to correct for temperature and pressure. 



From the formula s= \/ —j^- • — , we get for the velocity of 



air corresponding to two different conditions, if we neglect the 



c 

 variations of - as inconsiderable, 



i 

 s:s n 



?0= Vj : \/| = ^ ! ^0= V% T : s/§to To, 



H being directly proportional to the pressure p per square metre, 

 b inversely proportional to the volume v, and pv = kT, if T is the 

 absolute temperature, and k a constant depending on the pres- 

 sure and temperature, as has been shown in a previous commu- 

 nication*. 



If we take as the mean value of H corrected for aqueous va- 

 pour the number 0-744, we get by the formula above given, 



4=1-00032. *r = l-00065, and hence 4 1 = l-0034; 



4 76 = 1-00029, k l % = 1 -00065, „ C 7Q = 1 -00028 ; 



whereby the departures from the laws of Mariotte and Gay- 

 Lussac are allowed for. 



Placing the absolute zero at —273°' 15 C, which is its most 

 accurate value, calculated from the properties of hydrogen f, we 

 have 



For the 27th of June . . . T = 284*31, 



„ 28th „ ... T = 284-15. 



By substituting these values, we find for the velocity of sound, 



27th of June . . . 332'82 metres. 

 28th „ ... 331-91 „ 



Difference . = 091 



* Pogg. Ann. vol. cxvi. p. 429. " On the departures from Mariotte's 

 law in the real gases." 



f Poggendorff's Annalen, vol. cxvi. p. 434. 



