304 



On Hypsomeirical Measurements. 



[No. 4. 



Postscript. 

 It may be here remarked, — 1. That the formulae (10) and (11) 

 give very approximate results only when the pressure is above half an 

 atmosphere, but taking lieguault's value of the tension of vapour 

 at 32° Faht., we have 



7.426375 (T — 32) 



log/ = 1.25793 + , 



422.5743 -f (T — 32) 



which gives a maximum error of 0.025 in. at 122° Faht. 



2. That the quantity a, or the fraction of saturation may be easily 

 determined with very considerable accuracy from the formula — 



log a = 1 — 0.0170571 (t — t) + 0.0000289866 (* 8 — t 8 ), 



where t is the temperature of the air reckoned in degrees Fahren- 

 heit from freezing-point, and. t the dew point reckoned in the same 

 manner. 



3. That to the constants L and a in the general formula for the 

 determination of heights by the barometer, and to which I have 

 assigned the values 60369.15 feet, and 0.002039, respectively, 

 different investigators have assigned various other values. The 

 principal of these are as follows :— 



L, in. feet. 



Deluc, 



Schuekburgh, 

 General Roy, 

 Trembley, ... 

 Kamond, and Littrow, 

 Lindenau, ... 

 Poisson, 

 Baily, 



Bessel, 



5S958.2 

 60109.2 

 60032.4 

 60115.6 

 60345.6 

 60377.7 

 60161.8 

 60158.5 



60094.7 



a, for 1° F. 



0.002242. 



0.002425. 



0.002454. 



0.002462. 



0.002222. 



0.002222.* 



0.002222. 



0. 002083. 

 J 0.002222, or 

 I 0.002027. 



* Lindenau followed Euler and Oriani in supposing the temperature of the 

 air to diminish in harmonical progression through a series of heights increasing 

 in arithmetical proportion. His form of the term depending upon the tempera- 

 ture was — 



1 + 



t+t'— G4 (t— t') ! 



900 810,000 



t and t' being in degrees Fahrenheit. Lindenau's Tables (Gotha 1809) were in 

 some respects the best published in the early part of this century. 



Calcutta, Ydth August, 1858. 



