18 



cient of temperature of the magnet was determined at Moulraeiu, 

 and yielding the same results at other stations, is considered satis- 

 factory as regards accuracy. The range of the thermometer at 

 Moulmein was upwards of 35° ; and in the middle of the day, in 

 the tent, the heat was almost insupportable, being upw^ards of 105°. 

 The oscillation of the horizontal force is much greater at Moulmein 

 than at any other station. The minimum oscillation is at Singapore, 

 and increases both northward and southward. During the Survey the 

 portable bifilar was compared with the large Observatory bifilar, and 

 the results are given. The angle of torsion employed was always 

 the same, equal to 60° ; and the threads by which the hollow cylin- 

 drical magnet was suspended were the same during nearly the whole 

 of the Survey, having been in use for upwards of three years. 



The barometer w^as observed at every station. At the principal 

 stations the standard w^as in use, and at the others the portable, from 

 the greater trouble and risk attending the landing the large baro- 

 meter. The curve of the barometer, corrected to 32°, is exceedingly 

 regular, the time of maximum and minimum being identical for 

 every station on the Survey, viz. 21 or 22 hours for the maximum, 

 and 3 or 4 hours for the minimum ; the oscillation at every station 

 amounting to about one-tenth of an inch. The curve of the ten- 

 sion of vapour, as determined by the dry and wet bulb, is irre- 

 gular,, which is communicated to the barometric curve when ap- 

 plied to it; but this irregularity may be owing to the very short 

 time the instruments were observed at some of the stations ; and for 

 the purpose of ascertaining whether this really was the case, I pro- 

 jected the curves of the barometer, corrected to 32° of temperature, 

 at some of those stations where observations had been carried on for 

 more than a month, and likewise, in addition, corrected for tension 

 of vapour, thus giving the oscillation of the column of dry air. 

 There is certainly not the same regularity perceptible as in the oscil- 

 lation of the barometer, yet there is considerable uniformity in the 

 oscillation of the pressure of the column of dry air, the maximum 

 generally occurring at 19 or 20 hours, and the minimum at 2, 3 or 4' 

 hours. The range is likewise considerably greater. 



The tension of vapour was generally a minimum at 18 liours, 

 when it amounted to 0*8 of an inch. It then increased to 2 hours, 

 when it might amount to 0*9 of an inch, and then gradually dimi- 

 nished, having but one maximum and one minimum in the 24? 

 hours. In the islands of the Archipelago the air is nearly saturated 

 with moisture, and at Singapore the maximum difference between 

 the dry and w et bulb at 1 or 2 p.m. amounted to not more than 7°, 

 and then gradually and uniformly diminished till sunrise, when the 

 difference was rarely more than a degree. There appears to be 

 one maximum and one minimum of the dry and wet bulb thermo- 

 meter, the former at noon or 1 p.m., the latter at 18 or 19 hours; 

 the greates^t and least differences between the two thermometers oc- 

 curring, as has been observed, likewise at these hours. 



In addition to the above, a standard thermometer by Newman 

 was observed ; one maximum and one minimum occur in the twenty- 



