324 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
The mean value of has been employed in determining the value of X ; that is 
to say, the value of r^k found at a station is added to the results determined at 
previous periods, and a mean assumed as the true value of T^^k. 
(4.) Value of ^'5 — The value of P was determined for each 
needle, from the mean of many angles of deflection at the same distances. The 
following are the results of the mean value of P for the different magnets and the 
four declinometers. 
March, 1846, at Singapore, the value of P for D 5 and D 6, determined by the 
Observatory Declinometer, was —‘00309. 
June, 1846, at Sarawak, by the Induction Inclinometer, — 
The value of P for D 5 was +‘00320 
D6 +‘00169 
A 6 —‘024157 
A 7 -‘007276 
A 8 —‘00726 
A 9 —‘00335 
A 10 —‘00335 
C7 -‘00361 
June, 1848, at Sambooanga, in the island of Mindanao, by No. III. Declino- 
meter, — 
The value of P for D 5 was —‘00148 
A 7 —‘01642 
A 8 -‘00900 
A9 —‘01218 
A 10 -‘01407 
December, 1848, at Singapore, by No. III. Declinometer, the value of P for 
A 8 was . . —‘00930 
A 9 was . . —‘01059 
A 10 was . . —‘00932 
and by the Observatory Declinometer the value of P for A 8 was —‘00751. 
Remarks . — The observations of deflection are exceedingly numerous, and it is to 
be regretted that some of the time expended on them was not bestowed on the more 
complete determination of the coefficients ; but, as the angles of deflection were ex- 
TTl 
ceedingly small, it was deemed advisable to multiply observations for the value of^ 
as much as practicable. The needle was not always vibrated on the same day on 
which the experiments of deflection were observed, yet care was taken that it should 
be vibrated at the same time at which the deflection was observed ; and in low lati- 
tudes, subject to trifling disturbances, there is a greater change in a few hours on the 
