THE HEART OF THE ANTARCTIC 



took place in the lower atmosphere but also those 

 which took place in the higher strata of the atmosphere. 

 Erebus, with steam and smoke always hanging above 

 it indicated by the direction assumed by the cloud what 

 the upper air-currents were doing, and thus we were in 

 touch with an excellent high-level observatory. 



The instruments under Adams' care were as com- 

 plete as financial considerations had permitted. The 

 meteorological screen contained a maximum ther- 

 mometer, that is, a thermometer which indicates the 

 highest temperature reached during the period elapsing 

 between two observations. It is so constructed that 

 when the mercury rises in the tube it remains at its 

 highest point, though the temperature might fall 

 greatly shortly afterwards. After reading the recorded 

 height, the thermometer is shaken, and this operation 

 causes the mercury to drop to the actual temperature 

 obtaining at the moment of observation; the thermo- 

 meter is then put back into the screen and is all ready 

 for the next reading taken two hours later. A mini- 

 mum thermometer registered the lowest temperature 

 that occurred between the two-hourly readings, but 

 this thermometer was not a mercury one, as mercury 

 freezes at a temperature of about 39° below zero, and 

 we therefore used spirit thermometers. When the 

 temperature drops the surface of the column of spirit 

 draws down a little black indicator immersed in it, 

 and if the temperature rises and the spirit advances 

 in consequence, the spirit flows past the indicator, which 

 remains at the lowest point, and on the observations 

 being taken its position is read on the graduated scale. 

 By these instruments we were always able to ascertain 

 what the highest temperature and what the lowest 

 temperature had been throughout the two hours during 

 which the observation screen had not been visited. 



200 



