The accompanying tables furnish a few data respecting the periodical oscillations of the barometer, and the heating power of the sun's rays at a station within the tropics. They contain also some other observations usually supposed to be connected with the movements of the barometer. As they refer to a period of eight months only, no general conclusions regarding the climate can be deduced from them, and there-fore it was thought unnecessary to give a mean at the foot of each column.
Moulmein or Maulamyne, the principal station in the Tenasserim provinces, is situated in 10° 30′ N. L. and I believe about 97° 30′ E. L. It may be considered at the level of the sea, for the river, on the bank of which it lies, has free communication with the sea not eight miles to the westward, besides its more distant mouth at Amherst to the south. The observations were made at the height of thirty or forty feet above the surface of the river.
The barometer employed was a portable one of the syphon kind, and therefore required no correction except the reduction of the observations to a common temperature. The sound produced by striking the mercury against the top of the tube indicated that there was no air interposed. In making the observations, precautions were used to obviate the effects of friction between the tube and mercury. The barometer, also the wet-bulb thermometer, and one exactly similar for ascertaining the temperature of the air, were made by Mr. Robinson, of London. The thermometers were graduated to quarters of a degree of Fahrenheit's scale. The maximum and minimum thermometers were made by Mr. Adie, of Edinburgh, whose plan of introducing naphtha, above the mercury, in the former instrument, is completely successful in preventing the retraction of the index. The actinometer,[1] an instrument invented by Sir J. Herschel, was made by Mr. Robinson. It was observed only at apparent noon, and the glass plate in front of the bulb was always placed at right angles to the direction of the sun's rays. In making an observation, a board, just sufficient to intercept the direct rays of the sun, was held at some distance by an assistant, and the rise of the instrument during one minute was noted ; the board was then suddenly withdrawn, and the rise during an equal interval again noted; the rays being once more intercepted, an observation similar
- ↑ See Reports of the British Association, &c. vol. ii. p. 379.
