TABLES FOR DETERMINING HEIGHTS IvH 



Table 6^ represents values obtained from the expression within the 

 parentheses and Table 68 represents values computed from the latter factor, 

 taking 0.98 g^ as equal to 9.60 for a close approximation of the denominator. 

 This table thus gives increments of geometric height which are applied as 

 corrections to values obtained from Table (ij for stations whose acceleration 

 of gravity at sea level differs from 9.80. The side argument is dynamic 

 height by intervals of 1000 dynamic meters and the top argument is g^, accel- 

 eration of gravity, by intervals of o.oi 7;;/sec.- Interpolations must be made 

 for dynamic heights which are not in even thousands and for values oi g 4, 

 lying between those given at the top. 



Table 69. Difference of height corresponding to a change of O.i inch in the 

 barometer — English measures. 



If we differentiate the barometric formula, page xlvii, we shall obtain, 

 neglecting insensible quantities, 



(/Zz= -26281-^(1 +0.002039(^-32°)) (I+/3), 



in which B represents the mean pressure of the air column dZ. 

 Putting dB = 0.1 inch, 



2628.1 



dZ=- 



^i +0.002039(^-32°) j(i+^), 



B 



The second member, taken positively, expresses the height of a column 

 of air in feet corresponding to a tenth of an inch in the barometer under 

 standard gravity. Since the last factor (i+j8), as given on page xlviii, is a 

 function of the temperature, the function has only two variables and admits 

 of convenient tabulation 



Table 69, containing values of dZ for short intervals of the arguments 

 B and 6, has been taken from the Report of the U. S. Coast Survey, 1881, 

 Appendix 10, — Barometric hypsouictry and reduction of the barometer to sea 

 level, by Wm. Ferrel.^ 



The temperature argument is given for every 5° from 30° F. to 85° F., 

 and the pressure argument for every 0.2 inch from 22.0 to 30.8 inches. 



This table may be used in computing small differences of altitude, and, 

 up to a thousand feet or more, very approximate results may be obtained. 



1 Due to the use of a slightly different value for the coefficient of expansion, Prof. 

 Ferret's formula, upon which the table is computed, is 



2628.4 , 



dZ= ^ 



I1+ 0.002034 (e - 32°) j (I + /3). 



