F 2
The scale value of the Dines-Baxendell instrument was determined in the month of May, 1918, by means of a gauge constructed at the Observatory. It appeared to be correct within the probable error of observation, which was about 1 mile at a velocity of 80 m.p.h. increasing to 3 miles at 10 m.p.h.
Gap Rock Anemograph.--In the month of July a Dines-Baxendell anemograph was erected at Gap Rock. The records indicate defects in the instrument which it is hoped it will be possible to remedy shortly.
Thermometers.-All thermometers in use were compared with the Kew Standard in winter and summer.
Richard Thermograph.--The base lines laid down on the Richard thermograms from the hourly readings of dry and wet bulb rotating thermometers show irregularities which it is difficult to attribute to the exposure, the thermograph being placed in a well-ventilated double-thatched shed, 25 feet long by 20 feet wide, with gabled roof sloping from a height of 9 feet at the ridgepole to 33/4 feet at the eaves.
The thermograph is aspirated by a 12-inch fan distant 23/4 feet, which draws in the external air through a 11/4-inch pipe. The fan is operated by a contact on one of the electric dials closed from the 58th to the 60th minute of each hour. Prior to 1920, January 5, the contact was closed from the 59th to the 60th minute only, but it was found that one minute was not sufficient; on occasions the wet bulb pen was still falling at the 60th minute,
The registers are time-scaled electrically. An electro-magnet, operated by the hourly time signal, lifts the pens from the paper and clock work apparatus, adapted by Mr Evans in January, locks them until the 3rd minute when they are released and fall back on to the paper.
Sunshine Recorder.--In view of the interruption to the sunshine records caused by the Observatory wireless mast, a new sunshine recorder was obtained from Messrs J. Hicks and mounted on the south-west corner of the Main Building on January 6, 1921. Its records furnish the necessary corrections to those of the old instrument.
Peak Anemograph.--Signalman Osborne was in charge of this instrument from March 9 until May 31 when he resigned on account of ill health. He was replaced by Signalman McGrann on June 28. In the interval the sheets were changed daily by a computer from the Observatory.
It has not been possible to send a European Assistant to inspect the instrument as often as necessary, with the result that the records have not always been satisfactory.