294 CAPTAIN ELLIOT’S MAGNETIC SURVEY OF THE INDIAN ARCHIPELAGO. 
remarkable similarity of one year with another. As the sole object in giving these 
Singapore tables, was to determine the times of extreme easterly and westerly decli- 
nation, in the southern magnetic hemisphere near the line of minimum intensity, the 
results of the Singapore Observatory magnet are not in this instance given in 
minutes of arc, but in scale divisions ; one scale division being equal to 40"'/ of arc. 
Table A. — Pages xii to xlvii contain the results of the declinometers at the sixteen 
stations in the Archipelago. The stations are given proceeding from the most northern 
to the most southern : the observations themselves are omitted. At the top of every 
double page is printed the name of the station, with its latitude and longitude ; the 
mean astronomical time at the station ; and the value of one scale division in minutes 
JJ 
of arc, multiplied by the coefficient of torsion or 1 + p; the value of which is so 
trifling as not to affect the small diurnal changes of the magnet ; and the zero of the 
month, which is the scale division of the magnet at that hour at which the absolute 
determination of the magnetic declination wms made, usually at 9 a.m. The results 
of each instrument are contained in five lines ; the first, the sums of the scale readings ; 
the second, the means ; the third, the diurnal changes, from the mean of the month* ; 
the fourth, the range or oscillation of the needle, from its minimum or most western 
position ; and the fifth, the diurnal declination. 
Curves. 
The curves of the declinometer are given in Plates IV., V. and VI. Part 1 of 
Plate IV. contains the curves of the declinometer at those stations where observations 
were made during the spring and summer ; Part 2 of Plate IV. and Part 1 of Plate V. 
the winter curves ; Part 2 of Plate V. the equinoctial curves. The two Plates are 
drawn to a scale of 1' of arc to 0*35 of an inch, and Plate VI. contains the Singapore 
curves, which are drawn on a scale of 0''68 of arc (the value of one scale division) 
to 0’35 of an inch. In the three Plates the zero line is the line of the magnet’s most 
westerly position. The curve rising denotes a movement of the north pole of the 
magnet eastward. The curves themselves show, by the description of dotting, to 
which season they belong. 
As the station curves have to be compared separately with Singapore, it will be 
preferable to consider first the principal changes of the Singapore curves shown in 
Plate VI. In Part 1 of Plate VI., which gives the mean curve of each month for three 
years, it appears that the minimum or westerly declination occurs at Singapore in 
December at 19 hours ; in January at 20 ; in February at 21 ; in March (equinoctial 
month) a slight retrogression to 20 ; in April at 21 ; in May at 23 ; in June at 21 ; 
* The mean of the month being the mean of the whole number of observations ; where there are but nine- 
teen hours of observation, and these principally in the daytime, the mean of these for a mean temperature 
would unquestionably he too high; five of the hours of the night being omitted, the mean of the nineteen 
observed hours would be greater than the true mean ; but this is not the case with the magnetic declination, 
the range being exceedingly small at night, and usually close upon the mean position of the needle . 
