136 Dr. Schroeder van der Kolk on Gases. 



this, however, is not the case. Masson found the velocity of 

 sound in hydrogen to be 401 metres against 333 in air ; and 

 from the formula for the velocity of sound, taking the density 

 of aqueous vapour at -|, and designating by y' and 7 the values 



of — in the case of aqueous vapour and air, we get 



401 2 :333 2 = f/:7, 

 from which 



7 ' = 0-90637. 



The quantity of moisture present in the air during the experi- 

 ments was T Jy x £ = r £g of the air. 

 Hence 



1487 + 0-90637=l*4128 x 149, 



y = l-4137±0-0008 



for dry air at 0° and 0v6 metre pressure. 



Taking the value of the velocity of sound as certain to yooo* 

 the corresponding limits of 7 = 1*4113 and 1*4161. 



It is clear, from what follows, that this value of 7, which really 

 is calculated for 0°, may without error be regarded as valid for 

 4°, for which temperature the above formula is calculated. 



2. Regnault found for the specific heat of air 



between 



-30° and + 10° 



0*23771 





„ 100 



0-23741 





„ 200 



0-23751 



In the calculation, c x was taken =0*2375, from which is ob- 

 tained 



Cl -c = 0-06947. 



3. From the formula found in § III. we have 



die rlk 



~ = ~= 0*0000060526 K. 

 at (it 



4. Further, r=27-15, p = 0*76x 13595-93= the pressure in 

 kilogrammes on the square metre. 



5. From the formula for air at 4°, we get 



£=1-0002995x29-2443; 

 and further, since p = 13595h (h= the barometric height), 

 dk dk 



dp 13595^ 



= -0-00000269K. 



