CHAPTER II. 



TEMPERATURE. 



Instruments and Methods. 



Instruments and their Exposure.-The exposure of the thermometer screen at Cape Evan« 

 could not have been better. Immediately behind the hut the land rose rapidly to a smaU 

 hill 64 feet above sea-level. The top of the hill, called Windvane Hill, was so exposed 

 to the wind that it was always quite free from snow even after the severest blizzards Here 

 he screen was mounted on four stout posts well bound together and secured firmly into the 

 kenyterock The thermometers were about five feet above the ground, but the latter sloped 

 away on all sides so that the temperatures measured were practically free-air temperatures 

 In the screen were (a) a mercury dry bulb thermometer, (6) a mercury maximum thermo- 

 meter, (c) a spirit minimum thermometer; and (d) a bimetallic thermograph. 



Short^l rr°^"'^iJ" '^" ''"" "'' "" "'^'"'''^ commercial instrument made by Messrs. 

 Short and Mason. The pen was actuated by means of a bimetalhc coil and marked in the 



:t::ZrVjT \rr' '''''■ ''^ -^-^^ ^^^-^'^^ ^'' t^^m^o^.,^. in polar climat 

 were met. When the temperature fell below about -30°F. the clock stopped in spite of all 

 ^01 having been cleaned out of the bearings; also the whole instrument became coked u! 

 wi h driven snow dunng blizzards. These were not faults of the thermograph, which was a 

 plendid instrument to work with. The bimetallic control was very strong,'the s ^s tivenes 

 of the instrument was very uniform over the whole scale and remained constant thr ug t 

 The heat capacity was small so that rapid changes of temperature were registered. 



It was realised in England that we should have difficulty with the thermograph in the 

 screen A thermograph was therefore designed which would register inside the" hut "vhere 

 the clock and other moving parts would not be subject to the severe outside conditions 



bra s tube through which air could be drawn by an electric fan. This was fixed on to hi 

 north-east side of the hut, and a very narrow lead tube, passing through the wa 1 o 



^hin ;r;2 • T' Z ''' ''''-' ''''' ''''''' ^^^^ ^ ^P-^ -™- -"Gained 

 mthm a movable iron piston floating on mercury inside the hut. To the piston the pen 



bu b was lead every four hours, so that the record did little more than register the change 



cS^Tut ir\r : T:r ^* '--' ^^^ ^'^^^-^ '-^ -- --^ *° ^^-- ^^^ past t,: i 



col, but It was found that it made practically no difierence whether the fan was in 



Crandiiorsf^;'^ '"''r'^'' ^'^^ ^^" ^'- - '-^-^ -^^»- T^« i-trument w 

 Sluggish and not so well exposed as the thermograph in the screen 



