NOTES AND QUERIES. 
229 
If there were two observers, they would of course work simultaneously, 
one in the valley and the other on the hilltop, to guard against such ma- 
terial change of temperature or pressure as might take place while a single 
traveller was climbing. 
Example II. — If the traveller desire to know his elevation above the 
sea and has no simultaneous observations to refer to, he must assume the 
pressure at the sea-level to be at its average, viz. 30 inches, and make the 
best guess he can at what would be the temperature of the air ; the tem- 
Eerature decreasing, on a rough average, 1° for each 300 feet elevation, 
ict us suppose it in the above case to be 52° ; then the height of Mj above 
the sea is thus worked out : — 
^=52 
t'=¥) ^+/'— 64 28 
A„~-0=9560 ^+^^=92^^"^ 90 0 "900 
^aW sea^^] 98^8 9560x^^=11x28 about = 308 
The following tables refer to S, and explain themselves. They are 
the only ones that have to be applied to an aneroid or to a sympieso- 
meter : — 
Table I. Table II. 
Correction for the difference of 
gravity in various latitudes. Cor- 
rection positive from lat. (f to 
45"", negative from 45° to 90°. 
Table for decrease of gravity in a verti- 
cal, acting on the density of the air — 
always additive. 
Latitudes. 
Height of Aneroid at Lower 
Station. 
Approxi- 
mate dif- 
ference of 
o 
0 
90 
0 
10 
80 
o 
20 
70 
0 
30 
60 
o 
40 
50 
Approxi- 
mate dif- 
ference of 
inches. 
16 
inches. 
20 
inches. 
24 
inches. 
28 
leTel. 
level. 
feet. 
16,000 
feet. 
10,000 
feet. 
6,000 
feet. 
2,000 
1,000... 
5,000... 
10,000... 
15,000... 
20,000... 
3 
13 
26 
39 
52 
2 
12 
24 
37 
49 
2 
10 
20 
30 
40 
1 
7 
13 
20 
26 
1 
2 
5 
7 
9 
1,000... 
5,000... 
10,000... 
15,000... 
20,000... 
feet. 
2 
8 
16 
24 
31 
feet. 
1 
5 
10 
15 
20 
feet. 
1 
3 
6 
8 
11 
feet. 
0 
1 
2 
3 
3 
The aneroid may be briefly described as follows : — 
The weight of a column of air, which in the ordinary barometer acts on 
the mercury, presses in the aneroid on a small round German-silver box, 
both surfaces of which are corrugated in concentric circles, to improve the 
elasticity of the metal. The indications are thus obtained without the use 
of mercury or any other fluid. 
The new aneroid, which has been so favourably received and extensively 
patronized by members of the Alpine Club, is the result of a series of ex- 
periments carried on continuously for several years. The first point ac- 
complished was the perfect compensation of the instrument for tempera- 
ture. This was efiected by introducing a compound bar of steel and brass 
