320 Mr Galbraith's Barometric Measurements of Heights. 



In this rule no notice is taken of the terms in the series above the first, as 

 it is supposed that the heights to which it is applied are moderate, such as 

 2000, or 3000 feet. If the height exceed this, but not much surpass 5000 

 feet, the second term ought to be retained, which may be easily done in round 

 numbers, in the following manner: — 



Suppose that the barometer at the lower station is about 30 inches, and 

 that at the upper 23 inches, then the fraction formed from their difference 

 divided by their sum, simplified if possible, being squared, and the denomina- 

 tor of this multiplied by three, will give a fraction, of which the value being 

 taken of the approximate height already found, and added to it, will give the 

 true height. 



30 — 25 _ 5 1 1 }_ \ 1_ 



Thus, 30 + 25~55~ll'''""ll -^11 ^ 3 ~ 363' 



Hence, if ktto part of the approximate height be added to itself, the sum will 



be the true height sufficiently near for almost any purpose. It will generally 

 be found, however, that this last correction in most cases that occur in prac- 

 tice, is too small a quantity to merit much attention. 



The following examples are given for the purpose of illustration : — 

 Example I. The following observations to determine the height of the 

 Peak of Teneriffe, were made on the 8th of September 1824, by Lord Napiei", 

 Captain R. N., and communicated by Captain William Robertson, R. N. 

 Height of the barometer at Santa Cruz, 40 feet above the level of the 



sea, 30.164 inches. 



Attached and detached thermometers, . . . . 80° Fahr. 

 At the summit of the Peak, the barometer stood at . • 19.530 inches. 

 Attached and detached thermometers, .... 65° Fahr. 



B = 30.164, T =80°, < =80° 



h = 19.530, t' = 55 , t' = 55 



B — 5 = 10.634 r-./^ 25 / + «' = 135 . . . 135* 



0.45 = 60 



B + 6 = 49.694 2.42 300 



8100 



X. = 2.87 48400 



■r-r'=r 25 



5G500.0 



1435 B — 6 436.01 reversed. 

 674 



565000 



correction = — 71.75 33900 



1695 

 226 



B + 6 = 40.694)600821(12090.4 

 * *•• 49694 _ 71.8 



+ 40.0 



103881 



99388 12058.6 



Appr. height. 



4493 

 4472 



21 



