546 BESSEL ON BAROMETRICAL 



This is the most convenient form of the equation (11.) for use. 

 It cannot be abbreviated further \vithout giving up the power of 

 bringing into the calculation the quantity of aqueous vapour 

 contained in the atmosphere, as shown by the psychrometer at 

 each station. The tables for facilitating the computation may 

 also be so arranged, as to render quite inconsiderable the labour 

 of taking the aqueous vapour properly into account. 



11. 



I will now explain the auxiliary tables. They are construct- 

 ed logarithmically, like the small and very convenient tables 

 of Gauss ; but are rather more extensive, because they permit the 

 result to be computed on either supposition of A = 0'00375 or 

 = 0*003648, and also because they enable the influence of the 

 aqueous vapour to be taken into account more completely than 

 is done by the formula of Laplace. 



If we denote 



log {log 6, -logb/} by B, 



. (»-r.')w ■ • ''y^'' 



i byG, 



then is the logarithm of h' — h 1 



= B + log V + log V + log G. 

 Table I. contains the value of 



, ,, - 9397-74.400-l7(l + A-T) 

 log V = log 399.17-rr 



calculated in the first column for k = 0-00375, and in the last 

 column for k = 0-003648. Its argument is 2 T = t +t,. The 

 second column contains 



1 72-67. lO'"'^"'"'^' 



log W = log ^,j^.^y_^,^. 



a single column is sufficient for log W, as the difference in the 

 two values of k does not influence the last decimal. If we de- 

 duct from the tabular value of log W the half sum of the loga- 

 rithms of bi and bj, the remainder is the logarithm of 



(g + «0 W 



^^{b,b;) ' 



