330 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
sity. Sambooanga and Nicobar are about forty miles north of the line of no dip. 
The angle which the line of least intensity makes with the meridian is nearly a 
right angle. 
Lines of Variation. 
The first attempt which I made to determine the lines of equal variation was un- 
satisfactory. From 120 equations of condition combined by the method of least 
squares, I obtained results quite at variance with the actual fact. 
I then broke up the observations into three groups, one to the extreme west, com- 
prising the observations taken in Sumatra, one in the centre comprising the observa- 
tions taken in Java, and the third group to the east. The results thus obtained are 
more satisfactory, for the line of equal variation in the longitudes and latitudes over 
which the Survey extended is a straight line for a very short distance only. 
1st, or Eastern group : — 
o i 
At a mean latitude = 2 03 North. 
At a mean longitude =113 53 East. 
And mean variation = 1 23 East. 
The line of equal variation forms an angle of N. 52° 51' E. to S. 52° 51' W. with the 
meridian, and the rate of progression, or the value of r, is — 0'‘0346 the geographical 
mile. 
2nd, or Sumatra group : — 
o / 
At a mean latitude = i 36 North. 
At a mean longitude =100 36 East. 
At a mean variation = 1 35 East. 
u= - 82° 06', 
and r=-l-'0545 ; 
so that the variation increases as we proceed northerly, at the rate of -{-'0545 the 
geographical mile ; the line of equal variation forming an angle of N. 82° 06' E. to 
S. 82° 06' W. 
3rcl, or Java group : — 
o / 
At a mean latitude = 7 03 South. 
At a mean longitude =108 51 East. 
At a mean variation =+0 35 East. 
The value of r=0''145. 
The value of mz= — 89° 24', 
so that the line of equal variation in Java forms with the meridian an angle of 
N. 89° 24' E., and proceeds at the rate of 0'T45 the geographical mile. 
The lines have been laid down on the charts nearly in accordance with the fore- 
going results. 
