CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 327 
The eleventh column contains the altitudes of the stations above the sea level. 
Unfortunately, during- the survey of Java, I had no barometer with me. 
Table I. 
Table I contains the observations made at sea ; the inclination determined by Fox’s 
Dip Circle have already been noticed. The meteorological observations, consisting of 
the temperature of the air and of the sea, were taken when practicable, at 15, 18, and 
21 hours, at noon, and at 3, 6, and 9 p.m. The observations of the temperature of the 
sea were made in the following manner : — the thermometer was placed in a bucket 
of sea-water, allowed to stand for a few minutes whilst the other instruments were 
observed, and the thermometer was read off whilst its bulb was still immersed. 
The Table contained at pages clvi and clvii requires no explanation. 
On the Direction of the Isoclinal and Isodynamic Lines, and the Lines of Equal Varia- 
tion or Magnetic Declination. , 
On the Isoclinal Lines. — The observations of dip or inclination have been combined 
for the position of the isoclinal lines, their mean direction, and their mean distance 
apart; they have been formed into four different groups. 
1st Group. — Singapore, Borneo, and Java, afford forty stations ; and if we call ^ the 
dip at the central position, u the angle which the isoclinal line passing through the 
central position makes with the meridian, and r a constant coefficient, which deter- 
mines the rate of increase in a direction perpendicular to the isoclinal line ; and we 
put 
r cos u=.x 
r&\nu=y, 
we may make equations of condition of the following form : 
ax-\-by — 'b — 'd, 
where a and b are coordinates of distance in longitude and latitude of the several 
stations from the mean, expressed in geographical miles ; S' the inclination at these 
several stations, and S the mean dip. 
Then from this group we obtain, the results alone being given, 
o ! 
At a mean latitude . = 6 17 South. 
Mean longitude =108 55 East. 
And mean dip . . =— 27 01‘5 South. 
0?= — 0-132 3/=-fl-935 
r=-l-T-940 and m=-86° 06'. 
The axes of coordinates are throughout assumed positive when taken to the north 
and west; so that as we proceed to the north, the dip increases at the rate of l'-940 
perpendicular to the isoclinal line which forms an angle of N. 86° 06' E. to S. 
86° 06' West. 
