124 
Aneroid Barometer. 
The result of this Table seems to be that, for practical pur- 
poses, the ratio of 1 degree or inch of the barometer to 1000 
feet of elevation may be taken as a mean proportion at ordinary 
elevations. 
The most favourable time for using the Aneroid is when the 
air is still and uninfluenced by disturbing causes, as a change of 
pressure or of temperature would produce corresponding errore 
when only one instrument is observed. But a very near approxi- 
mation to tlie truth may be obtained by the use of two barometers 
which have been compared and adjusted ; the stationary one 
should be read every hour, while the other is in the field, and the 
usual correction for temperature applied. 
By this simple instrument, aided by the railway sections 
which intersect the kingdom, the physical features of any country 
may in a short time be accurately determined, and a better 
knowledge obtained of its climate as influencing its agricultural 
capabilities and prospects. NICHOLAS Whitley. 
Truro, Z\st Maij, 1854. 
Note. — Tlie aneroid, to be really useful, requires to be in the Lauds of 
persons aware of its liability to mislead, and kuuwiup;, like Mr. Whitley, how 
to guard against this. All aneroids, like mercurial barometers (though from 
another cause), do not move at the same rate. 174, 172 are mercurial re- 
ductions, corresponding to l'J4, 212, 198, and 222, given by aneroids, taken 
from A to B and back to A again, the real height being 172. Another simul- 
taneous pair were 2017 and 1817, another i)air 1772 and 1690, off different 
instruments. Headings taken on a journey are very amusing, but they must, 
as ]\Ir. Whitley's example shows, be counterpoised by a return journey. The 
same height, in a recorded observation in MS., came out 148 in the morning 
journey and 415 in the afternoon return journey. But the correction for 
barometric variation l.irought the first to 373 and the second to 370. Two 
careless observers would have respectively struck by the 148 and 415, or con- 
demned their instruments. 
The same aneroid will also work at a different rate under different degrees of 
barometric pressure, and the more careful makers endeavour to get its action 
most perfect in that part that is most likely to be used. From some unex])lained 
cause, tlie same aneroid has worked at different rates at one time from "what it 
has at another, and they are liable, with sudden jerks, to shift their whole 
reading permanently to the extent of 
The Table extracted from Belville's work was computed by him on the 
supposition of the thermometer being at 55". Galbraith's Tables, costing only 
2s., should be in the hands of all who wish to use the barometer for deter- 
mining heights carefully. Following the best formulaj, his Tables are com- 
puted for freezing-point, and a table of corrections given for the temperature of 
the air. Upon a height of 1000 feet the correction might easily be in a sharp 
frost a suhtructiou of 10 feet, or an addition of 100 feet in a hot summer's day. 
Notwithstanding the above remarks, the aneroid is a most interesting com- 
panion ; but it is not too much to ask that those who do not know how to guard 
against mistakes in the use of it will be very careful not to put out as accurate 
or trustworthy tlie simple results of its uncorrected readings at the rate of 1000 
feet to the inch. — liemarks hy Mr. Troytc. — T. D. Acland. 
