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
| Lower Station |  | 30·385 | inches. |
| Upper Station |  | 30·025 | |
|  | Difference | ·360 |
| Divided gives | ·360 | = 327 feet. |
| ·0011 |
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:—
| Â | Inches. | ||||||
| Reading at | 10 a.m. |  | 29·89 | ||||
| " | 5 p.m. |  | 29·76 | ||||
|  | Mean |  | 29·825 |  | Table I. | 1010 | |
| Upper Reading |  | 26·81 |  | " | 3796 | ||
| Â | Difference | Â | 2786 | ||||
| Mean Temperature 55°·5, gives in Table II. | 1·048 | ||||||
| Â | 2920 | ||||||
| Lat. 55° N., gives in Table III. | ·9991 | ||||||
| Â | 2917 | ||||||
| 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.
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