BAH 



traacd from the elevation found by the general rule, \vhen 

 the mercury at the upper ftation is colder than that at the 

 lower. For in this cafe the mercurial column at the upper 

 ftation \vill appear too fhort, and the prefliirc ot the ;itmo- 

 fphtre too fmall ; fo that the elevation m the atmofpherc 

 will appear greater than it really is. Confequently the 

 rule for this correction will be to multiply 0.0000444 by the 

 degrees of dilVerence between the mercurial temperatures 

 at the two ftations, and to add or fubtraft the produdl 

 from the elevation found by the general rule, accordmg as 

 the mercury at the upper ftation is hotter or colder than 

 that at the lower. If the expanfion be conlidered as vari- 

 able, the logarithmic difference correfpondlng to this ex- 

 panfion f«r the mean temperature of the two barometers 

 may be taken. Tiicfe logarithmic differences are contained 

 in !h ollowing table, carried as far as 1 1 3 \ beyond which 

 it is not probable that any obfcrvations will be made. The 

 number for each tempcratura is the difTcrcuce between the 

 logarithms of 30 inches, of the temperature 32, and of 30 

 inches expanded by that temperature. 



BAR 



Sir George Shuckburgh has ^iven the following table 

 for the expanfion of mercury by heat. 



T.^BLE III. 



