16 Mr. Nixon o?t reducing Barometrical Registers to the 



of the barometer in feet above the level of the sea ; and t the 

 observed temperature of the air. 



Formula No. I. — Reduction of the pressure h to its value 

 at the standard temperature of 32° Fahr. = h'. 



additive or subtractive as T is below or above 32° Fahr. 



No. 2. — Reduction of the pressure at 32° Fahr. = h' to its 

 value at the level of the sea =: H. 



log. H = log. h' + 



56054. 





2Vo. 3. — Reduction of the observed pressure h to its value at 

 the level of the sea, and standard temperature of 32° Fahr. = H. 



log. H = log. h± - ;-~^ ' 



the upper or lower sign to be used as 69"8 &c. + « is greater 

 or less than 2-2 &c. x T *. 



Explanation of the Use of the Table. 



For formula No. 3. — 1°. To the observed temp, of the air 

 add ~-Q part of the alt. which term the mean temp. 



2°. With the mean temp, enter the col. A, and take out the 

 corresponding quantity in col. B, which add to the altitude. 



3°. With the mea7i temperature for the first column take 

 out the corresponding quantity in column C, which midtiplij 

 by the height of the detached thermometer. 



4°. Note the difference of this jnvduct and the sum last 

 found, marking it positive or negative as the sum is greater or 

 less than the jproduct. 



5°. Multiply this difference by the quantity given in the co- 

 lumn D corresponding to the mean temperature found in the 

 first column, and divide the product by 1000. 



6°. To the logarithm of the observed pressure, (corrected 

 for capacity and capillarity,) add or subtract, according to the 

 sign prefixed to the difference, the quotient just found, which 



* Approximatively, log. H = log. h + ~ 



56054. 



will 



