1826.] Measurement of Heights by One Barometer. 85 



Observations. 



(No. 2.) Horton Bridge S'' 40™ .... 29-220 (46) 



Pen-y-gent. . . 12 10 .... 27-640 (35) 33 

 Horton Bridge 16 40 .... 29-250 (42) 

 (No register of the thermometer was kept at Horton Bridge.) 



Reduction, 8fc. 



Pressure at Horton Br. at 16" 40™ . . 29-250 (42) 

 Add for 4° of difference of the interior 



therms. (46) - (42) -01 1 (5ee Table 1 .) 



Pressure at 16" 40™ . . 29-261 (46) 



Ditto 8 40 ..29-220(46) 



Interval 's ±) -041 



•005-1 rise per hour. 



Pressure at 8" 40™ 29-220 



Rise in 3 30 -018 



Pressure at 12 10 = 29-238 (46) ' 



Subtracting from the pressures the constant quantity -552, we 

 have for calculation, 



Horton Bridge (29-238 - -552) = 28-686 (46°) 

 Pen-y-gent. . . (27-640 - -552) = "27-088 (35) 33 



Tables II, III, and IV. — The observations being prepared 

 for calculation, enter Table II. with the pressure at the lower 

 station, neglecting the last figure, and take out the correspond- 

 ing feet, &c. With the same pressure to the nearest inch, find 

 by Table III. the value in feet of the rejected figure (or thou- 

 sandth part of an inch*). To these two quantities, add the 

 feet, &c. answering to the height of the interior thermometer, 

 as given in Table IV". 



Find the corresponding quantities for the upper station, and 

 subtract their sura from that obtained for the lower one, and the 

 remainder will be the difference of altitude at 0° F. 



Then correct the sum of the detached thermometers for the 

 latitude as indicated in Table V, and multiply the corrected sum 

 by the altitude at 0° F. and the decimal fraction -00i2.t The 



• It will never cause an error of two feet in the calculation of the altitude to substitute 

 the last figure itself. Gross errors of computation may be detected by estimating -001 

 inch of mercury equal to one foot; I inch to 1000 feet, &c. See the calculation given, 

 vol. vi. p. '-i65, where the error exceeds 2000 feet. 



+ Substituted for — ■ = -00 11 962. The alteration will never cause a difference of 

 836 



five feet {additive) ia altitudes of lOOOO feet. 



