Measurement Of Heights By The Aneroid

For measuring heights not exceeding many hundred feet above the sea-level by means of the aneroid, the following simple method will suffice:—

Divide the difference between the aneroid readings at the lower and upper stations by ·0011; the quotient will give the approximate height in feet.

Thus, supposing the aneroid to read at the

r />

Lower Station   30·385 inches.
Upper Station   30·025
  Difference ·360

Divided gives ·360 = 327 feet.

As an illustration of the mode in which the aneroid should be used in measuring heights, the following example is given:—

A gentleman who ascended Helvellyn, August 12th, 1862, recorded the following observations with a pocket aneroid by Negretti and Zambra:—

Near 10 a.m., at the first milestone from Ambleside, found by survey to be 188 feet above the sea, the aneroid read 29·89 inches; about 1 p.m., at the summit of Helvellyn, 26·81; and at 5 p.m., at the milestone again, 29·76. The temperature of the lower air was 57°, of the upper, 54°. Hence the height of the mountain is deduced as follows:—

Reading at 10 a.m.   29·89
" 5 p.m.   29·76
  Mean   29·825   Table I. 1010
Upper Reading   26·81   " 3796
  Difference   2786
Mean Temperature 55°·5, gives in Table II. 1·048
Lat. 55° N., gives in Table III. ·9991
Table IV. 5
Difference of height 2922
Height of lower station 188
"Helvellyn 3110
In Sir J. Herschell’s Physical Geography it is given as 3115 ft.

So near an agreement is attributable to the excellence of the aneroid, and the careful accuracy of the observer.