the Temperature Corrections of Barometers. 



413 



inches and tenths of inches, each inch representing 100 millim., 

 whilst each millimetre of correction is represented on the 

 lower horizontal axis by two inches. A series of lines, each 



Fig. 3. 

 8° 10' 12° (4° 16° 18° 20' 22° 24° 26° 28° 30° 



4.0 MM. 



representing a difference of 2° C. of temperature, are then 

 ruled through the origin to the points on the upper horizontal 

 axis marked 8°, 10°, 12°, &c. The position of these points is 

 easily obtained from the formula 



(/3— 7) B^ = correction in millim., 



by substituting for t the values 8°, 10°, 12°, &c, for B, the 

 value 800, and for /? and 7 the coefficients of expansion 

 of mercury and the material of which the scale is made 

 respectively. 



