Of BAROMETRICAL MEASUREMENTS. 107 



23. THIS formula includes the correction to be made for 

 that inequality of the expanfion of air by heat which depends 

 on its compreffion, and which was defcribed at the yth and 8th 



articles. The firfl term of the formula, viss.p lof. t is the differ- 

 ence of the tabular logarithms of b and (3. The fecond, viz* 



fmplog.^ is M. DE Luc's correction, and the fame that was 

 R 



already invefligafced, 17. The third, viz. 



l -* lS- r X P log.- is the correction for the above mentioned 



2 7 F 



inequality of- expanfion. It is of a form very convenient for 

 computation; for the former correction being rr 



fmpkg.^ we need only multiply it by --&<? to have 

 the third term of the formula, or the correction required. It 

 mufl be remembered, that % fignifies the hyperbolic loga- 



t b 



nthm of r. 

 X 



THE exact amount of this correction cannot be known, till 

 I* be defined by experiments on the expanfibility of air under 

 different degrees of compreflion ; thofe which General ROY has 

 made, though excellent, not being perfectly fufEcient for that 



purpofe. If we fuppofe p , and if, as an example, we 



2 



take b 29 inches, and (3 24, y being 29.5, then we will 



&P f* 



find log. =. .22 nearly, which, multiplied into , or into 



, is j-g nearly, and this multiplied into M. DE Luc's 



correction, gives the correction for the compreflion. The 

 former is, therefore, to be diminifhed by jgj before it be applied 



O 2 tO 



