SUPPLEMENT TO THE HONGKONG GOVT GAZETTE OF 17TH JAN., 1885. 59
obs is narrowed by slits, and the same arrangement is made to obtain the photographic record the barograph, but the photograph exhibits in this case two curves, which represent the the dry and damp bulb thermometers interrupted by the two-hour lines. The record of the plated vertically under that of the dry, so that there is only one time-scale. One or two which to measure are obtained by allowing the light of either lamp to shine through in either of the frames, in which the slits are cut.
photographic sheets obtained from the thermograph are treated exactly as those obtained ph. When they are dry the distances of the points on the curves from the zero line all of glass scales graduated to degrees. The temperature in either case corresponding He is obtained daily by comparison with the simultaneous readings of the thermometers which are corrected before being entered in the thermograph journal. The degrees on scales should be larger than the degrees on the thermometers in the proportion, in which magnified by the photographic lens. This has been attained in case of the damp bulb, on the dry bulb scale must be multiplied by 0.980 in order to represent the readings A correction is applied for this before the readings are entered on the tables thly reports.
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to prevent by any possibility a mistake in the date of the photographic sheets, the anal date are written on the back of every sheet, as it is removed from the cylinder.
tuent the Crown Agents for the Colonies had ordered the barograph and the thermo- The memograph through the Meteorological Office. The tabulator, reading scales ently ordered at my suggestion as well as the pluviograph. Unfortunately a large paper had also been supplied by the Secretary to the Meteorological Office, who was not -bromide paper had for years been successfully adopted in India. Now the necessity ensitising every photographic sheet bas caused a deal of trouble during the damp and The sensitised sheets were found not to keep for two days on the barrel. The sheets changed every day. Even the iodised sheets did not keep for any length of time. ulised sheets could be sensitised with any certainty of success, and this added enormously a great part of the time of the second assistant being taken up by this work. Even when ention was taken, the result was not nearly as good as during the winter. Tannin, as abel by Chambers, was tried, but made no improvement here. A supply of MORGAN & ngono-bromide paper bas now been ordered, and thus the trouble of iodising and sensitising will be saved.—Another cause of occasional failure rests with the Kerosine lamps, but the being so much more sensitive, the lamps are not likely to give any trouble, when the new intro luced. It may also be found possible to secure Kerosine oil of superior quality. No ly was encountered in keeping the damp bulbs constantly wetted, but occasionally the were found to be dry.
The clocks of the barograph and the thermograph were rated by shortening the pendulums, dud inconvenient to shorten them sufficiently. The outstanding error was corrected by pieces of iron and a few small leaden weights on the flat upper surfaces of the bobs, sequently kept constant by adding or removing one or more of the small weights. at proved so satisfactory, that the clocks when accurately started one morning were in number of enses found as accurate next morning, and the error seldom exceeded nover 45 seconds.
mograph was crceted in the course of January and worked without interruption since It is erected on a turret, built of strong teak-wood timber, fastened to the roof of the ive iron bolts. The turret rises 8 feet above the flat roof of the main building. This instrument registers the number of miles traversed by the wind and also its direction. of a "ROBINSON's anemometer of large size, the cups of which are 45 feet above the ground we mean sea level. The shaft carrying the cups is supported by friction balls running p of the direction shaft and terminates in an endless screw, which working through dives a cylinder in the turret, round which a thin strip of brass forming a screw is Rond another larger cylinder, which is driven by a clockwork, is wrapped the metallic the space traversed by the wind is recorded by the screw-shaped pencil, which rests of the weight of the cylinder round which it is wrapped. The pencil has only one Ender and its pitch is 23 inches long, equal to a scale of 50 miles printed on the paper. ial factor-3 is adopted in our anemometric records. Whenever from further investiga- liable factor, dependent on the velocity of the wind shall have been determined for exactly similar construction, it will be easy to alter the figures in cur tables, but the gruent is so perfect that no allowance need be made for friction-In order to obinin stinct trace of the direction of the wind, the vane consists of two wind mill wheels, their axis at right angles to the wind. With any change they move and carry with them tube, which contains, but is not connected with, the velocity shaft and acting through moves another thin screw-shaped pencil, which registers the direction on another part paper. The pitch is equal to that of the velocity pencil and equal to a scale of the cardinal Compass printed on the paper. The clock moves the cylinder on which the paper is
per hour.
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