CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 317 
Index Correction. 
True dip on shore from nine needles . . . 11°02'’7 
Dip from needle B. (Fox) as above .... 11° 28'‘0 
Index correction +25‘3 
This instrument Colonel Sabine, R.A. had the kindness to send out to me, and 
[ used it whenever an opportunity offered, but the Schooner was so small that it 
was difficult to take observations of inclination when there was any sea on. The 
needle B. was never removed from the box, and advantage was taken at every station 
of applying to the dip a fresh index correction. Fox’s Dip Circle, sent out overland, 
was very roughly handled on its way out, so that the circle was no longer concentric 
to the axis of the needle. The observations were taken on a gymbal stand, the dip 
oircle being leveled as accurately as possible, and twenty readings taken with the 
face of the circle to the east, and the same number with the face of the circle to the 
west. The inclinations at sea contained in the General Table, are the means of several 
groups of observations ; for the dip being observed whenever it was calm, three or even 
five observations were taken repeatedly during the day when the weather permitted. 
General Table, and Reduction of Observations to one common Epoch. 
The General Table of Inclination on shore and at sea is given at pages cxxxvii, 
Dxxxviii and cxxxix. The whole of the observations are reduced to one common 
jpoch, viz. the 1st of January, 1848. At the Singapore Observatory observations 
were taken at two different periods, and with great care. 
At the commencement of 1848 the dip was —12° 56'‘8 
At the commencement of 1849 the dip was —12° 59''4 
The difference nearly, of one year ... = — 2'*6 
These are valuable chiefly from the superior character of the instruments and 
lipping-needles. But going back to the first establishment of the observatory, the 
mean dip of the needle was — 
At the end of 1841 — 12°43'‘3 
At the end of 1848, or commencement of 1849 . . — 12°59''4 
-16'-] 
giving for the yearly change — 2'’3. 
The secular change at Madras can likewise be determined ; for from the mean of 
;wenty-two observations taken in July 1840, 
The mean dip of the needle was -|-7° 13' 40" N. 
Twenty-nine observations in July and August 1849, gave -|-7° 37' 42" 
Total difference in nine years . . -1-24' 02" 
