F 2
Factor for converting the actual run of the Beckley Anemograph cups to velocities recorded by the Dines Pressure Tube Anemograph.
Factor (Dines ÷ Beckley).
Month Mean 1910-1920 1921 January 1.87 1'83 February 1'49 1.89 March 1'91 1.83 April 1:46 1.85 May 1.60 1.96 June 1'93 1.78 July 1.93 1.89 August 1'77 1.83 September 1'99 1.97 October 1.69 1.78 November 2.02 ... December 1'77 1.92 Year 1'96 1'74Gap Rock Anemograph.—This instrument was dismounted and brought to the Observatory to be overhauled in November. A leak in the float was repaired, the vane lightened and a vertical tail added, with stream line cross section as recommended by the London Meteorological Office.
Owing to its exposed position the vane was designed to withstand exceptionally heavy gales, with result that, owing to its weight, it was very sluggish. This caused erroneous records not only of direction but velocity also, as the true velocity is only recorded when the vane is pointing in the direction from which the wind blows. It follows that in estimating the amount of turbulence in the atmosphere from records of Dines Anemographs the sensibility of the vane must be taken into consideration, the alternate lulls and gusts shown on the anemograms being partly due to the vane not responding to changes of wind direction, and to the fact that the vane is continually oscillating on either side of the wind direction, only remaining parallel to the wind for a short time.
Thermometers. All thermometers in use were compared with the Kew Standard in winter and summer.
Richard Thermograph.—This instrument worked satisfactorily during the year, though the base lines as laid down from the hourly eye observations of rotating thermometers still show irregularities, except on dull days with small range of temperature. The period during which the fan automatically aspirates the thermometers has been further increased to 5 minutes i.e. from the 55th to the 60th minute of each hour. The effect of the fan on the dry and wet bulb readings for the year 1921 is being measured. The results may modify the figures given on page 16 of the 1918 report.