;V2 Mr. J. Burgess on the Measurement of Altitudes 



4. Now from equation (1) we have 



T-T' 

 W ~~logB-logB' ; 

 and from Regnault's Table of Tensions, as corrected by Moritz, 

 we obtain 



T =100° C B =760 millims dB = 27-212397, 



T' = 80 B'=354'616, 



by means of which we find for the standard boiling-point 



^=zgB = l§= 64 - 307626 ' 

 and between 80° and 100° C, 



S« = log reo-kg 354-616= 60 ' 413836; 



and since between these points n is found to vary almost exactly 

 as the temperature, we may write for boiling-temperatures 

 between 80° and 100° C, 



7i = 64-3076-0\L9474(100°-T). .... (4) 

 Hence 



770 millims. _ 5-13493(100°-T) 



l0g B~ " 230-215 + T ' ' " * ( } 



Combining (2) and (5), and introducing the value of L for a 

 standard atmosphere at 0° C, the approximate height above the 

 point where water boils at 100° C. is expressed in metres by 



100°— T 

 A m =94568 m x 8 - 3 . 215 + T ; (6) 



and approximately by 



A m =285 m -54(100-T)+0-955(100-T) 2 . . . (7) 



5. Allowing for the difference of pressure between 760 millims. 

 and 30 inches, we may represent the pressures on the English 

 barometer corresponding to boiling-temperatures between 176° 

 and 212° F. with great exactness by the formula 



log B = log 30 in. -0-00864,1566 (212°- T) 



-0-00001,43365 (212°-T) 2 -0-00000,00316,l(212°-T) 3 .(8) 



This formula, which is of the form first used by Biot, will 

 give the same results as the more complicated one of Begnault, 

 when T lies between 172° and 216° F. From this we may at 

 once derive the height in feet of the point at which water boils 

 at T° F., viz. 



£=521-684 ft. (212°-T)+0-8655(212 o -T) 2 + 0-0019(212°-T) J 



