306 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
for measuring approximately the degree of humidity in the atmosphere ; and Colonel 
Sykes, F.R.S., has mooted the question in a very interesting paper on the Meteoro- 
logy of India, which has been lately published in the Philosophical Transactions : 
one of the sources of error supposed to be peculiar to this instrument, although 
easily remedied if discovered, is the too close proximity of the wet bulb to the dry 
bulb, the consequent depression of the latter, the difference of the two thermometers 
or the value of d consequently diminishing, and the resulting tension of vapour 
greater than it ought to be. I do not know the exact distance that the two bulbs 
were apart in Cary’s little instrument ; at most 2 to 2^ inches, and both fixed to 
one stem. The following are the results of a comparison between the Standard 
Thermometer and Dry-Bulb Thermometer at all the stations ; and it will be seen, on 
inspection of the following Table, how very slight are the differences between the 
two thermometers*. 
Station. 
Month. 
Mean by the number of hours. 
Difference. 
Standard 
Thermometer. 
Dry 
Thermometer. 
Standard— Dry 
Thermometer. 
Moulmein 
April 
88*4 
88-3 
+ d-i 
Madras 
September ... 
85-2 
85-2 
0-0 
Nicobar 
February 
80-9 
80-5 
+ 0-4 
Sambooanga 
>^ay 
82-0 
82-2 
+ 0-3 
Pulo Penang 
January 
81-7 
81-2 
-f 0-5 
Pulo Binding 
January 
82-6 
83-2 
-0-6 
Sarawak 
June 
79'6 
79‘6 
0-0 
July 
78-8 
78-9 
-0*1 
August 
78-7 
78-8 
-0*1 
Keemah 
.Tune 
81-5 
8M 
+ 0-4 
Pulo Peesang 
January 
81-5 
80-8 
-fO-7 
Singapore 
December ... 
79*8 
80-2 
-0-4 
Padang 
October 
80-5 
79-7 
+ 0-8 
November ... 
80-8 
80-2 
+ 0-6 
December ... 
81*3 
80-6 
+ 07 
January 
81-7 
80-9 
+ 0*8 
Bencoolen 
September ... 
79-3 
79-3 
0*0 
Batavia 
November ... 
80-3 
80*2 
+ 0-1 
December ... 
79-8 
79-7 
+ 0-1 
January 
80-1 
79-8 
+ 0*3 
February 
79-6 
79-5 
+ 0-1 
March 
81-3 
81-2 
+ 0-1 
April 
81-3 
8M 
+ 0-2 
May 
81-2 
80-9 
+ 0-3 
June 
81-0 
80-7 
+ 0-3 
Cocos 
September ... 
79-2 
79-5 
-0-3 
Standard Barometer and Portable Barometer^ and Adjustments. 
At the principal stations the large Standard Barometer was in use ; but at some 
the Portable Barometer was observed, from the greater trouble and risk attending 
* At Padang the differences are the greatest, and as these appear to he constant at the same station, they 
are probably due more to the relative position of the Standard Thermometer and Dry Bulb, than to the proxi- 
mity of the latter to the Wet Bulb. 
