Royal Society. jf49 



the Dutch settlements' of Sambas, Pantianak and Succadana on the 

 western coast. 



In Sumatra four months of observation at Padang, besides a mag- 

 netic survey comprising about thirty stations. I crossed the equator 

 here as well as at Pantianak in Borneo. 



At Singapore I compared the portable instruments with the fixed 

 instruments of the observatory, besides determining the horizontal 

 intensity and dip, which had not been accurately determined pre- 

 viously from insufficiency of means. 



At the Cocos or Keeling Island:^, six weeks of observation. 



At Sambooangan, in the Island of Mindanao, upwards of a week. 



At Keemah in Celebes, the same. 



At Penang, the same. 



At Moulmein, the same. 



At the Nicobars, the same. 



At Bencoolen in Sumatra, the same. 



I will now mention the instruments and the mode of observation at 

 the observatories. The following instruments were registered every 

 hour from 3 a.m. to 9 p.m. Two declinometers, and latterly a third 

 made by Jones; a bifilar magnetometer and its thermometer; a 

 standard barometer and its thermometer by Newman ; a standard 

 thermometer and a dry and wet bulb. 



On the survey, I employed for the observations four dipping- 

 needles ; a portable declinometer with altitude and azimuth instru- 

 ment for the declination and for latitude; a sextant, artificial hori- 

 zon and chronometer for the error and rates of the watch, which 

 was but a poor one. 



1 began work generally at 6 a.m., put up the portable declinometer, 

 and allowed the brass weight and stirrup to swing for a couple of 

 hours thoroughly to take the torsion out of the thread, adjusting it 

 from time to time so that the stirrup might ultimately take up a po- 

 sition in the magnetic meridian ; during this period I took the dip. 

 At 8 A.M. I took sights with the sextant, and putting in the collimator 

 magnet, I adjusted the altitude and azimuth to it, and took altitudes 

 and azimuths of the sun, three on the limb direct, and three on the 

 limb reversed, noting the reading on the horizontal limb ; at the same 

 time this gave me the reading of the true meridian ; the magnetic 

 axis of the collimator magnet was then read off; these observations 

 were usually completed by 9| a.m. : by 11 a.m. I had finished my 

 observations for horizontal intensity. The small collimator magnet 

 being suspended, the large collimator magnet was placed at four dif- 

 ferent distances east and west, and the deflecting collimator magnet 

 was then vibrated and 300 oscillations taken. 



At 11 A.M. I observed altitudes and azimuths of the sun with the 

 altitude and azimuth instrument for equal altitudes. At noon I took 

 circummeridional altitudes of the sun, three with the limb direct, 

 and three with the limb reversed, for latitude; at 1 p.m. I again took 

 altitudes and azimuths. 



By equal altitudes from the mean of the times, I was enabled to 

 check the results given by the sextant for time; and by the azimuths 

 corresponding to the equal altitudes, I checked the observations for 



