MEASUREMENT OF HEIGHTS BY THE BAROMETER, gg 



XIII. 



On the Measurement of Heights by the Barometer. In a 

 Letter from a Correspondent. 



To Mr. NICHOLSON. 



SIR, July ljlh, 1809. 



j| HE method of finding heights by the barometer bids Finding 

 fair to be of the greatest practical utility; especially since j^^'V 

 the improved construction of portable barometers, and the great practical 

 invention of more compendious modes of calculation than ullllt ?- 

 those formerly in use, have considerably diminished the dif- 

 ficulties, with which it was at first attended. 



It would be desirable, however, if the necessary calcula- Desirable to 

 tions could be still farther simplified : for it must frequently hayethecalco- 



, -• . , «•!«■• lations still far- 



happen, that observations or the heights or the barometer ther simplified, 



are made by travellers at times, when the mind, distracted 



by a variety of objects, or borne down by the fatigue of the 



body, may be ill calculated for even a moderate degree of 



exertion. 



For this purpose .the following tables have been calcu- 

 lated, which, with little more than the mere trouble of in- 

 spection, will give the result true to the nearest foot. They 

 may be printed on the surface of a common card, so that 

 their bulk cannot be the least inconvenience to a traveller. 



Table I. Contains altitudes in feet answering to every tj 3e of-thefc;!- 

 tenth of an inch of the height of the barometer from 25 to lowing tables. 

 31 inches. 



Table 2. Contains the proportional parts to be deducted, 

 for every additional hundredth of an inch, corresponding 

 to the heights of the barometer marked in the first co- 

 lumn. 



Hence to find the approximate elevation of one station 

 above another, nothing more is necessary, than to find from 

 Tables 1 and 2 the elevations corresponding to the ob- 

 served heights of the barometer, and subtract the less from 

 the greater. 



It would not be difficult to construct tables, which should 



give 



