OBSERVATIONS TAKEN IN INDIA. 
337 
could any of them or their means have been safely taken to express normal condi- 
tions? Pi'ofessor Orlebar, in his Meteorological Observations at Bombay for 1846, 
gives proofs of the necessity for caution in the use of the wet bulb : in the first place, 
he was obliged to abandon the records of the air-thermometer attached to the wet bulb 
from the irregular depression of the former, by the cold of the evaporating surface of 
the latter; and in the next place, on the comparison of the action of two wet bulbs, 
one inside the observatory and the other outside, he records discrepancies in March 
ranging from 3°’2 plus to 2°'6 minus ; the comparisons in April and May exhibited 
minor discrepancies, excepting on the 27th of April at the 18th hour, when the dis- 
crepancy was 3° minus. Professor Orlebar having used Daniell’s hygrometer 
simultaneously with the wet bulb for eight months in 1846, the means of cotnparison 
are afforded, and the following Table exhibits the results, I have taken the two daily 
observations at 9'’ 12"^ a.m. and 3'* 12™ p.m. on the first day of each month for the com- 
parison. 
Dates. 
Barometer. 
Months. 
Day. 
Local 
hours. 
h 
m 
in. 
January 
1st 
9 
12 
30-092 
3 
12 
29-942 
February ... 
1st 
9 
12 
29-987 
3 
12 
29-879 
March 
1st 
9 
12 
30-003 
3 
12 
29-878 
April 
1st 
9 
12 
29-899 
3 
12 
29-804 
May 
1st 
9 
12 
29-834 
3 
12 
29-731 
June 
1st 
9 
12 
29-748 
3 
12 
29-668 
July 
1st 
9 
12 
29-615 
3 
12 
29-583 
August 
2nd 
9 
12 
29-728 
3 
12 
29-678 
September ... 
1st 
9 
12 
29-733 
3 
12 
29-666 
Thermometers. 
Dew-point by 
Tension of 
vapour by 
Fraction of saturation 
or per-centage of 
moisture in the air by 
Wet 
Daniell’s 
Wet 
Daniell’s 
Wet 
Daniell’s 
Dry. 
Wet. 
bulb. 
hygro- 
meter. 
bulb. 
hygro- 
meter. 
bulb. 
hygro- 
meter. 
O 
79- 
72-8 
O 
70 
66-8 
0-726 
0-635 
75 
83-5 
73-3 
68-6 
69*9 
0-695 
0-724 
62 
64f 
76-3 
71-6 
69-4 
73-0 
0-713 
0-801 
80 
90 
80-4 
72-0 
68-05 
71-0 
0-682 
0-751 
67 
74 
79-6 
73-5 
70-8 
75-1 
0-746 
0-856 
75i 
86f 
83-3 
75-6 
72-35 
75-5 
0-785 
0-867 
70 
78 
84-4 
75-4 
71-6 
73-5 
0-765 
0-814 
66 } 
70| 
87-6 
74-2 
68-15 
73-1 
0-684 
0-803 
54 
63i 
92-5 
80-8 
76-55 
80-8 
0-897 
1-027 
60f 
69 
96-8 
80-5 
74-4 
76-9 
0-838 
0-907 
50 
54 
83-2 
80-8 
80-0 
81-5 
1-000 
1-049 
90 
94f 
90-7 
84-4 
82-45 
81-5 
1-081 
1-049 
7f. 
75 
81-4 
80-0 
79-2 
78-5 
0-976 
0-935 
90 
88i 
81-8 
79-0 
78-0 
78-8 
0-939 
0-964 
88| 
91i 
81-2 
79-9 
79-45 
78-6 
0-984 
0-958 
94f 
92 
84-4 
81-0 
79-85 
77-5 
0-996 
0-925 
86f 
80i 
84-0 
80-0 
78-6 
77-5 
0-957 
0-925 
84i 
83-8 
80-0 
78-7 
76-3 
0-959 
0-890 
85 
79 
These observations having been made by the instructed and practiced manipulators 
of the Bombay Observatory, claim to be worthy of confidence; but we find ourselves 
in doubt which of the two sets to use for the correction of the barometer and to de- 
termine the real amount of moisture in the atmosphere. It would appear, that when 
the depression of the wet bulb and of Daniell’s hygrometer is small in the monsoon 
months, their results do not differ very widely, the wet bulb however giving a higher 
tension of vapour and greater per-centage of moisture or fraction of saturation in the 
atmosphere than Daniell’s hygrometer; but in the cold and hot months of the year 
2 X 
MDCCCL. 
