708 PROCEEDINGS OF SECTION E. 
APPENDIX. 
Barometric Levelling Formula. 
Mercurial Barometer, with Brass Scale. 
At Lower At Upper 
Station. Station. 
Observed height of barometer... oe pe: ee sh ho 
Ap temperature of mercury eas ins nes AR a 
35 3 of air (dry bulb) <5. fay t t’ 
_ a of wet bulb an aos 56 tro tw 
Height of mercury reduced to 32° Fahr. AS. sah H,. hy 
Vapour tension ofsaturation at temperature of wet bulb b b/ 
Altitude of lower station above sea-level = S 
Mean latitude of stations aA va = 
Earth’s radius in feet = 7 = 20,890,000 approximately. 
Difference of elevation of stations in feet = Z 
H, — H, }1-0-000 089 6(T - 32°) 
i ae }1- 0-000 089 6(T —32) | 
een: ersten Malicr |) au eet 199 Lay) 
140-001 O17 (¢+t' — 64) 5 (1+0-189  ) (+0189 Pa 
( 
He | , 1—0°000 084 (t—-tw) + 410-000 084 (”—t'w) | 
Z=60,159 log z- iS Sa | w et l w) XL 
X 
28, Z 
@e aD (1+ >) 1+0°002 606 cos 2 L 
For tables facilitating use of this formula see U.S. Coast and Geodetic 
Survey Report, 1881. 
