[ "O ] 



mufl retrench or add ,i of an inch from or to the obferved height 

 of a column of 30 inches, and on the fame principle it will 

 be found that a variation of each degree of the thermometer 

 above or below 550 expands or contrails the mercury ,00101333 

 of an inch in every column of the length of ten inches. The 

 mercury therefore ftanding at 30 inches, the corredion for each 

 degree of variation of temperature above or below 55*' is in the 

 proportion of ,1 of an inch to a variation of 33°; call this cor- 

 redion C. If the height of the mercury in the barometer alfo 

 varies from 30, call the obferved height A, and the correction 



fought X, then fay 30: A:: C: X, therefore _=X. To 



abridge thefe calculations a table has been conftruded on the 

 foregoing principles, which Ihews in decimals of an inch the 

 effedl of the expanfion or contradion for each fmgle degree of 

 the thermometer above or below 55" upon the number of inches 

 of ? marked in the firft column. 



TABLE 



Inches of ? 



To 



