340 RoijalSoekiij. 



.,c,,jThe, object which the author proposed to himself was the- deter- 

 mination of certain magnetic lines within the limits of the Surwyr; 

 the lines of no dip, and of the maxininm horizontal component soTf 

 the earth's force ; the minimum intensity of the total magnetic forces 

 and finallj-, the line of no declination. He was also desirous of obr 

 serving tiie variations of the magnetic elenients, and of ascertaining 

 whether the changes of the declhialion, of magnetic intensity, and 

 of the barometer, were uniformly similar over so large an area. 

 The fixed stations for this latter purpose were sixteen in number, 

 and the time employed at eacii station varied from a few days to 

 several months. They were spread over an area of 26° oi latitude, 

 and more tiian 40° in longitude, viz. from 16° latitude north to 12° 

 south, and from 80° to 12.5° longitude east. This part of the globe 

 coincides very nearly with the position of minimum total force. Of 

 the sixteen stations, nine Mere to the south of this line, three to the 

 north, and four in its immediate vicinity. Four stations were in the 

 islands adjacent to Singapore ; one in Borneo ; one in the island of 

 .Java; two in Sumatra; one in the island of Mindanao ; one in Ce- 

 lebes ; one at the Cocos or Keeling Islands, which was the most 

 southern station to which Capt. Elliot could venture ; one at Penang, 

 and one in its immediate vicinity ; one at Nicobar, an island in the 

 Bay of Bengal; one at Moulmein, which was the most northerly, 

 and one at iMadras, whicli was the extreme westerly, station. The 

 total number of days employed iu observing at the fixed stations 

 amounted to 496. The instruments employed at the fixed stations 

 were, for the changes of declination, sometimes three, but never less 

 than two ; and for the ciianges of the horizontal force, a bifilar mag- 

 netometer with a thermometer for registering the temperature of the 

 enclosed magnet ; a barometer, either Newman's standard or a por- 

 table, with their attached thermometers; a dry and wet bulb ther- 

 mometer for ascertaining the immidity of the atmosphere ; and a 

 standard thermometer. The observations were usually made under 

 canvas, and close to the sea-shore. There being usually but one 

 assistant, it was impossible to observe during the whole twenty-four 

 hours ; the hours of observation selected were therefore from 3 a.mj> 

 to 9 P.M. inclusive. In Borneo, and during the first four months in; 

 Java, there were three assistants, and observations were taken hourly.; 

 As these observations were made at the different stations in dif- 

 ferent seasons, it was necessary to have the observations of some 

 station for upwards of a year, for the purpose of instituting a com- 

 parison between the changes of one station with another. Tiiis was 

 more especially the case with tlie declination ciianges, as the times 

 of extreme westerly variation are continually altering. The curves 

 of changes of declination at Singapore were therefore projected 

 for each month of the three years 1843, 1844 and 1845, duringj 

 which time the observations had been made hourly ; and like.-); 

 wise for each of the four seasons ; by comparing with these theo 

 observations made during the Survey, the author was able to difj 

 stinguish the changes due to geographical position from those duer, 

 to the season of the year. •; 



