304 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
Curves. 
The curves corresponding to these Tables are laid down in Plate IX. ; but the 
standard thermometer for the dry bulb is substituted. The curves are drawn to a 
scale of 10° of temperature to 0'35 of an inch. 
Remarks. 
The curve of the dry thermometer consists but of a single progression, the mini- 
mum being usually at 6 a.m,, the maximum at noon. The curve of the wet thermo- 
meter consists likewise but of a single progression, its maximum and minimum 
occurring at the above times ; the diurnal variation of the tension of vapour at pages 
xc and xci at the different Survey stations is very irregular ; the curve usually con- 
sists of but a single progression, and is very similar to the wet bulb. The mini- 
mum is usually at 6a.m., the maximum being at noon; the greatest range extending 
from 0*1 to 0’26 of an inch of the barometer. The irregularity occasionally indicated 
may be owing to the shortness of the period during which the instrument was ob- 
served. At those places where the dry and wet bulb were observed for more than a 
month the curve is regular. Throughout the Archipelago the minimum of tension 
of vapour usually occurs at 6 a.m., the maximum being at noon ; a remarkable ex- 
ception to this takes place at Madras, where the minimum is observed at noon ; it 
appears to be explicable from the circumstance of the remarkable dryness of the air 
at Madras in August and September compared with that of the Archipelago generally ; 
the dry thermometer at Madras ranges 15°‘5 during the day from 6 a.m. to noon, or 
1 p.M. ; at which time it is at its maximum, as also the difference between the dry 
and the wet bulb. After 1 p.m. the dry thermometer gradually falls, and the differ- 
ence between the dry and wet bulb diminishes, whilst the wet-bulb thermometer is 
still rising, very slowly, till 3 p.m. ; consequently the tension of vapour increases so 
that the minimum elastic force occurs at noon, and the maximum some time in the 
afternoon. 
The mean elastic force of the tension of vapour varies from 0‘8 to 0*9 of an inch 
of the mercurial column. 
The range of the humidity in the atmosphere, given at pages xciv and xcv, shows 
a single progression only, the minimum being at noon, the maximum early in the 
morning; in some instances the air is saturated with moisture at 6 a.m. 
At Moulmein and at Madras, where the air was driest, and just previous to the 
N.E. monsoon at the latter and the S.W. monsoon at the former place, the mean 
quantity of humidity varied from 66 to 68 parts, complete saturation being 100; in 
the space included in the Survey the air is always loaded with moisinre, and it is a 
tolerable approximation to the truth to state, that throughout tne Archipelago the 
minimum quantity of humidity is O’/S, the maximum 0‘85, and the mean quantity 
0'80 ; complete saturation being =1*0. 
The following Table contains the stations, their latitudes and longitudes ; the mean 
