C H A P T K R III. 



WIND. 



Instruments and Methods. 

 Anemometers. — Three anemometers were used at Cape Evans. 



[a] A small Robinson anemometer having .3-inch cups on 7g-inch arms and calibrated to 

 the factor 2-73. This instrument was considered to be the standard instrument. 



(6) An anemometer also having the same size cups and arms, but so aiTanged that after a 

 certain number of revolutions an electrical circuit was closed for a short time. Wires were 

 taken from the anemometer to a recording instrument within the hut, by meaii.'-' of which a 

 pen, \\Titing on a drum revolved by clockwork, was raised a short distance every time the circuit 

 was closed. Thus a series of steps was drawn on the record each one of which corresponded 

 to a defbiite amount of wind. A time mark was made on the actual record every hour by 

 means of an electric current from the standard clock. The value of the \\ind amount corre- 

 sponding to a step of the record was determined at frequei\t intervals, by counting the steps 

 on the record corresponding to a day's run of the standard anemometer. Both of these 

 instruments (n) and (h) were mounted side by side on a wooden frame on the top of Wind 

 Vane Hill. 



(c) A Dines pressure tube. This instrument had been specially designed to meet the 

 difficult conditions of the Antarctic. The head had been so arranged that it could be easily 

 removed and cleared of snow, and the suction part of the head had been erected separately 

 from the vane. Also a reservoir had been inserted between the head and the fioat in 

 order to prevent any snow which entered the nozzle accumulating in the connecting pipes. 

 The instrument as designed in London was specially made by Mr. Munro of Cornwall 

 Road, London, and very kindly lent by him to the expedition. The head was erected at 

 the east end of the hut within which was the recording pai-t. The temperature withrn the hut 

 was generally above £i-eezing point, but it was found advisable to use petroleum as the liquid 

 in the cistern, as on one or two occasions the water and glycerine supplied froze. 



The change in design of the head proved a great success in practice. During blizzards 

 a cert.ain amount of snow accumulated just within the nozzle ; but every four hours, when 

 meteorological observations were made, this was cleared out and it was only in the worst 

 blizzards that any part of the record was lost omng to the nozzle becoming choked up with 

 snow. 



The exposure of this anemometer on the roof of the hut would not have been satis- 

 factory if it had been desired to use its record for obtaining true wind velocities, because the 

 hut was in the lee of Wind Vane Hill and therefore not exposed to the full velocity of 

 the wind. The records however have not been used for obtaining actual velocities, but only 

 for studying the ' structure of the wind.' The velocities recorded by the cup anemometers 



