in the Magnetic Survey give the resulting equations at a mean 

 latitude of 0° 09' north, mean longitude 10i° 44' east, and mean 

 dip 14° 40'"4) south ; the isoclinal line running from north 86° 39' 

 west to south 86° 39' east ; and the dip in the line at right angles to it 

 increasing at the rate of 1 ''953 for each geographical mile. .,f^u 

 -.iNearJy the same method has been pursued in laying down (thd 

 lines of equal horizontal force. In one group this line forms an 

 angle of north 67° 48' west to south 67° 48' east with the meri- 

 dian, and the line perpendicular to it proceeds at the rate of 

 •Q0082+9 for each geographical mile, the central station being iu 

 latitude 0° 38''5 north, and longitude 102° 26' east. In another 

 group at the central station 3° 40' south, and 106° 33' east, the 

 line of equal horizontal force forms an angle of 60° 57' vvith the 

 meridian, and increases at the rate of "0005855 for eafih geograplMT 

 cal mile on the perpendicular line. : ; '« 



The lines of declination have been laid down with reference to 

 the declination at each station individually, the particular form of 

 the lines rendering the method of grouping inapplicable. ; i,i ,;ii;',(i 



Total force. — The total force was not determined directly,, bufej^yr 

 the formula f=-h . sec i^, where /* is the horizontal intensity, i the 

 dip, and / the total force ; and as the dip changes rapidly, but 

 regularly, whilst the horizontal intensity changes slowly, but irregu- 

 larly, it is evident the lines of total force will follow in some de- 

 gree the regularity of the intervals between the lines of dip. 



The total force for each station was determined by the above 

 formula, and equations of condition, combined by the method of 

 leait squares, determined the direction of the isodynamic line, in 

 the mean latitude of 3° 05' south, Jongitude 106° 47'; where the 

 mean total force was 8-745. The angle which the isodynamic line 

 forms with the meridian is from north 85° 86' west to south 85° 36' 

 east, and increases southerly at the rate of •001073 for each geogra-; 

 phical milp. The line of least intensity, in the apace over which 

 the, Survey jv%f; parrj^jql, aippears tp )agre^.ftljno?t,e^aQtly.Jwi|th|ftl^§jUBei 

 of.npdip; ,,, ,.,;,. I,, i_: .i ,:•;;;,.- i-- ^-:, ;;;.., /lij...;; .i- .u-:M^f;.u! 

 ..To recapitulate briefly respecting the position of the principal 

 iipes. The line of no dip cuts the meridian at an angle approach- 

 ing a right angle, and near the parallel of latitude of 8° north in the 

 longitude of Singapore ; the rate of progression being almost exactly 

 two miles of dip to ono mile of latitude. The line of least total 

 force varies but little from the line of no dip, forming indeed a 

 somewhat larger angle with the meridian. The direction of the 

 maximunv horizontal force forms an angle of nearly 65° with the 

 meridian from north-west to south-east, but neither the maximum 

 horizontal nor the minimum total intensity appear to be, strictly 

 speaking, lines. In taking two stations having the same value, the 

 one to the north and the other to the south of the position of 

 greatest horizontal intensity, and dividing the distance between 

 them, it might be supposed that this would be the position of the line 

 ofgreatesthorieoutal intensity; but the maxinmm horizontal intensity 

 appears not to be a line, but a space or belt extending for a consi- 



Pkil. May. S. 1. Vol. 1. No. 4. April 1851. 2 A 



