the Barometric Formulce, ^c. 653 



Let 3, 3' be the temperatures (Fahrenheit) of quicksilver of the barometers 

 of the lower and upper stations, as shown by attached thermometers. 



Let/,/' be the actual elastic forces of vapour of water of the atmosphere 

 at the lower and upper stations, and very nearly equal to the elastic forces pe- 

 culiar to the dew-points of the lower and upper stations, as given by an approved 

 table of elastic forces (or tensions) of aqueous vapour, or otherwise obtained. 



Let Fi be the elastic force (or tension) of aqueous vapour, peculiar to the 

 arithmetic mean of temperatures of the atmosphere given by the detached ther- 

 mometers, as obtained from an approved table of elastic forces of vapour, or 

 otherwise. 



Let a be the mean fraction of saturation of the atmospheric column between 

 the stations of observation, assumed to be equal to the arithmetic mean of frac- 

 tions of saturation of atmosphere at lower and upper stations. 



Let %■/{//') be c ; £ being designated the hygrometric element. 



Let aFi be c (8'= 8 very nearly : vide Appendix). 



Let p(l + '^ he£. 



Letp'\l + m{T-T')\ = p'\l + n(U-:i')\ he B'. 



B and B' are, therefore, the values of ^, /3' (barometric observed pressures) 

 corrected for differences of the specific gravities of the quicksilver of the baro- 

 meters, arising from differences of temperature of attached thermometers, as 

 also from differences of gravity occasioned by height of one station above the 

 other. 



Let (H. C.) designate horary correction. 



Benny's General Forrmda, in its most General Form. 

 . = Cjl + fcos 201 }l-f^jjl+A:^'j log |^±(H.C.), Cent. 



.=.C|l-ffcos20|}n-?^jjl-|-Z(^'-^-32){log|^V(H.C.),Fahr. 



The character z in the above two formulae, as also in all the following 

 ones, replaces the character H as found in the formula; of pages 444 and 446 

 of this volume ; the character z is that employed by Poisson in his formula. 



