258 



Mr KELLAND, ON THE MOTION OF 



24. Let us apply this expression to Professor Robison's experiments 

 for dry air, considering it merely empirical : from tliis we obtain 



Z) = 2; 1.957 = 2(1 + a); 



.-. a = - .022, 



P=D\l - .022 {D - I)] ; 



Z) = 3, P = 3 (1 - .044) = 2.868, 



Z) == 4, P = 4 (1 - .066) = 3.736, 



n = 5.5, P = 5.5 (1 - .099) = 4.955, 



Z) = 6, P= 6(1 - .11) = 5.340, 



n ---- 7.62, P = 7.62 (1 - .1456) = 6.50. 



If we arrange these in a table with the measured results, we have 

 as follows : 



The first and third differ by .02, the rest are nearly accurate, so 

 that the empirical formula is not far from the truth. 



25. In the summation of the preceding series (22), we have only 

 retained the first terms of the various integrals, which amounts, in 

 fact, to substituting the fluent for the definite integral. On applying 

 this process to the expression for the velocity, it was shewn to be 



