RECORD AND DISCUSSION OF ATMOSPHERIC PRESSURE. 87 



The constant c is, therefore, + 0.159 mches, at a mean temperature 75°. 78 and 

 a mean barometric pressure 29.831. To deduce the coefficients m and n, the cor- 

 rection c has first been applied to the aneroid readings. The following differences 

 were then formed : B— {A + c), {A + c) — 29.8.31, and T— 75°.8. We then have 

 the 65 conditional equations : — 



1. 



o. 

 4. 



— O.Oig = +0.328 Hi — 10.8?i 

 —0.034 = +0.258 m — 3.8 n 

 — 0.072= + 0.168 m— 13.8 n 

 —0.039 = —0.012 m — 5.8 ?« 

 etc. etc. 



Their solution furnishes m and n. Making first the coefficient of n as great as 

 possible, bj addition and change of sign of the equation when necessary, we find 



203.4 n + 0.846 TO = +1.314 

 or, w= +0.00075- 0.004 771, 



and, in like manner, m results from the equation — 



12.56 TO + 4071= +1.190 



m = +0.072, and n = +0.0065 



Hence the formula for reduction — 



Inch. 



B = A + 0.159 + 0.072 (A ■ 



Inch. 



.29.672) + 0.0065 (T- 75°.8). 



To show the result by the formula in extreme cases, the following eight com- 

 parisons are here inserted. 



Inch. 



J Computed reading B = 29.92, same observed (31) = 29.93 



No, 



„ Q r Lowest temp. 



" 32) 



„ ^g| Highest temp, 



" 23| 



X 



\ 

 r 



^ f Greatest pressure -\ 

 ^ r Least pressure i 



29.41, 

 29.35, 

 30.03, 

 30.31, 

 30.35, 

 29.3.3, 

 29.23, 



These differences prove a sufficient approximation in the terms of the above 

 expression, and likewise leave no doubt that the indications of the aneroid may 

 generally be relied on to nearly within one-hundredth of an inch. 



To faciUtate the reduction, the following table of corrections has been calculated 



