Barometric Measurement of the Height of Cheviot. 76 



The first numbers agree nearly with our own observations, as 

 well as those of Dalton and others, made at moderate elevations 

 above the earth's surface ; the second with Ramond's height of 

 Col du G^ant from Geneva, which, for 10,000 feet, gives 277 

 feet, almost exactly the same as the Table, 278, from our for- 

 mula ; while Chimborazo, for about 21,000 feet, gives 400 feet, 

 a little less than the formula that assigns 420 feet for this height. 



In most works respecting this subject, the object of the wri- 

 ters has been to deduce a mean value to be applied generally, 

 and stating it as from 270 to 300 feet, which, by consulting our 

 Table, corresponds to heights of 10,000 and 15,000 feet, and, 

 consequently, must be wide of the truth in both very small and 

 very great heights. Our formula is, doubtless, of an empirical 

 character, but supported by an appeal to the most accurate ex- 

 periments that could be obtained ; and in that case will, it is 

 hoped, prove serviceable, till a better be obtained, though, from 

 its variable nature, we are aware that no formula will ever be 

 produced strictly applicable in every case. 



As the centesimal thermometer is frequently used, it has been 

 suggested that a formula for obtaining heights, when that in- 

 strument is employed, would be useful, it has been subjoined. 

 The small corrections for height, latitude, &c,, may all be con- 

 veniently simplified, and readily appended to the first part of 

 the formula, to render it general and complete, though they are 

 only wanted in great heights, seldom measured, and not to be 

 met with in Britain. 



1. For Fahrenheit's Thermometer. 



H = |48400 + 60(. + O j^ 1^ ^- {2.42+ ^} (.- ^) 

 -\-h (0.00268 4- 0.00268 cos 2 X + 0.00000005 h) 

 "in which H is the true height in feet, t the temperature of the 

 air by detached thermometer at the lower station, t that at the 

 upper ; t the temperature of the mercury in the barometer at 

 the lower station by the attached thermometer, r' that at the 

 upper ; B the height of the mercury in the barometer at the 

 lower station, h that at the upper, h the height, and 7^ the latitude 



2. For the Centesimal Thermometer, giving H in feet. 



H= |32260+110(< + <' I 3~* .-|4.56 + ^t£| (^_^) 

 + h (0.00268 + 0.00268 cos 2 X -h 0.00000006 h). 



