F 2
The scale value of the 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.
Dines Baxendell Anemograph for Gap Rock.--This instrument was received in September, and the scale value tested. It was found that when the float was weighted to give the scale value engraved on the sheet (Inɛ. = 0.1o,·06) the water encroached on the conical portion of the float. It is proposed to adjust the float until 1/4 of an inch of the cylindrical portion appears above the level of the water, and determine the scale value once a month under these conditions, measuring the records with an appropriate scale.
Plans have been prepared for the iron structure required for its erection on the lightkeepers' quarters at Gap Rock and it is expected that the installation will be finished in February.
Thermometers.--All thermometers in use were compared with the Kew Standard in winter and summer.
Thermograph.--The Richard dry and wet bulb thermograph has worked satisfactorily during the year. Its records, which are standardised by hourly readings of the rotation thermometers, indicate that the relation between the temperature in the thermograph shelter and in the open air is not constant throughout the day.
The records are time-scaled electrically. An electro-magnetic circuit is closed by a make-contact on one of the electric dials at the 60th minute of every hour and opened at the 3rd minute. The electro-magnet lifts the pens from the paper and thus interrupts the record for the first three minutes of every hour.
The thermometers are aspirated from the 59th to 60th minute of each hour by an electric fan operated through a special relay by a similar contact on another dial.
Sunshine Recorder.--The shadow of the wireless mast, erected in the summer of 1917, falls on the sunshine recorder for a few minutes in the afternoon from January 16th to March 29th and September 16th to November 28th. The mast has a skeleton frame, the ribs of which partially eclipse the sun and occasionally cause a slight loss of register. A more serious loss occurs when the sun passes behind the joints of the mast (which are steel plates 3 feet square) or when sun sets behind the mast. A list of corrections to the sunshine values in Tables V and IX of the Monthly Meteorological Bulletin, on account of this interruption, is given in the December Bulletin. The correction is never large enough to affect the values given in Table XI.
Peak Anemograph.--The naval signalmen who looked after the Peak Anemograph were withdrawn by the Naval Authorities in May. It has since been necessary to send an assistant from the Observatory to change the sheet. From motives of economy the sheet is only changed once in two days. The consequent overlapping of the register is objectionable but will, it is hoped, soon