IN PASSING THROUGH THE ATMOSPHERE. 
247 
well as those of the thermometers (which are all by good makers), are not recorded, 
but can hardly have an appreciable influence on any of the results about to be de- 
duced. 
60. The detached and moistened thermometers are reduced to Fahrenheit’s scale, 
and the absolute elasticity of vapour in inches of mercury, as well as its hygrometric 
state relative to absolute saturation, are calculated from Dr. Apjohn’s formula and 
tables*. The formula is 
e ' 87 0 
b_ 
30’ 
where t and t' are the readings (Fahrenheit) of the dry and wetted thermometer; 
e' the maximum elasticity of vapours corresponding to t' ; e" that corresponding to 
the dew-point ; b the observed height of the barometer in English inches'f~. The 
hygrometric observations have considerable interest in themselves owing to the ex- 
traordinary dryness of the air at the upper station, — a dryness, it is believed, alto- 
gether unusual even at that elevation ; being an elasticity of vapour at 7^ h a.m. of only 
*038 inch at temperature 39°, or ratio to saturation of ’148. This dryness must be 
considered as one of the peculiarly favourable circumstances of the present experi- 
ment. 
Table A. — Meteorological Observations at Brientz, September 25, 1832. 
Mean 
time. 
Appa- 
rent 
time. 
Barometer, 
French. 
Attached 
Therm. 
Reaum. 
Barometer 
in milli- 
metres. 
Attached 
Therm. 
Cent. 
Barometer 
at 0° C. 
mm. 
Detached 
Therm. 
Fahr. 
Moist 
Therm. 
Fahr. 
Diff. 
Elasticity of 
vapour in 
inches of 
mercury. 
Relative 
dampness. 
h 
m 
li 
m 
inches. 
lines 16 ths . 
— = -819 
442 V 
8 
2 
8 
10 
26 
10-8 
14-6 
727-51 
18-25 
725-06 
55-0 
51-8 
3-2 
•362 
9 
5 
9 
13 
26 
10-8 
14-7 
727-51 
18-38 
725-07 
58-1 
54-7 
3-4 
•401 
S = ’ 817 
10 
5 
10 
13 
26 
10-8 
15-0 
727-51 
18-75 
724-99 
60-5 
55-5 
5-0 
•395 
H = "743 
11 
3 
11 
11 
26 
10-4 
15-3 
726-94 
19-13 
724-38 
61-2 
56-5 
4-7 
•414 
i=-760 
11 
50 
11 
58 
26 
9-13 
15-0 
725-94 
18-75 
723-43 
65-5 
57-2 
8-3 
•386 
386 r. , 
628 ~ ® 1 5 
1 
1 
1 
9 
26 
9*14 
15-0 
726-10 
18-75 
723-59 
68-0 
59-0 
9-0 
•408 
m = -599 
2 
17 
2 
25 
26 
9-12 
15-5 
725-81 
19-38 
723-21 
68-4 
59-5 
8-9 
•418 
8 = - 606 
3 
2 
3 
10 
26 
9-11 
15-3 
725-67 
19-13 
723-11 
64-3 
59-5 
4-8 
•460 
4 
4 
4 
12 
26 
9-9 
14-9 
725-38 
18-63 
722-89 
64-2 
57-5 
6-7 
•408 
4 
38 
4 
46 
26 
9-8 
14-9 
725-25 
18-63 
722-76 
62-2 
58-8 
3-4 
•466 
I=- 828 
* In order to obtain tolerably consecutive results, it was found necessary to project graphically both the dry 
and moist thermometer observations. Nos. I. II. III. IV. Plate XVIII., and to run curves freely amongst the 
points. The values for the whole hours are thus obtained in Tables A. and B, and the elasticities of vapour 
for those hours are thence computed. 
t Supplementary Report on Meteorology, British Association Report, 1840, p. 98 ; and Royal Society’s In- 
structions. 
