IN WINTER QUARTERS WITH CAPTAIN SCOTT 237 



lecture with simple diagrams, which are reproduced in the figures on 

 p. 221. 



He started with an amusing instance of error in measurement. It 

 is an obvious principle that the measurement itself must not alter the 

 condition of the experiment. Thus, if you want to know the length 

 of your own trousers, you introduce an error if you bend down to 

 measure them ! 



There are three methods of measurement in general use — by pho- 

 tography, by moving a lens, and by various mechanical methods. 

 Lastly, the time must be accurately recorded, and this is usually done 

 by a chart carried on a rotating drum, which is clock-driven. The 

 whole apparatus being called a chronograph. 



In determining temperatures we need that of the air itself, and we 

 must eliminate the direct effect of radiant heat. Thus a thermometer 

 placed near a newly kindled fire records the access of heat long before 

 the surrounding air is warmed by the fire. Hence we must bring a 

 large quantity of air into contact with the thermometer. The method 

 while sledging is to use a " sling-thermometer." Here the thermo- 

 meter is enclosed in an aluminium case of which the opened lid forms 

 a handle, by which the thermometer can be swung rapidly for some 

 minutes in the air. 



In self-recording thermometers it is more usual to suck a large 

 quantity of air past the thermometer by means of a little fan, as shown 

 in Fig. B. 



If, however, a check is kept by frequent comparisons with standard 

 thermometers at the same place, this is not necessary. Thus the 

 thermograph at Wind Vane Hill consists of a bimetallic coil fixed at 

 one end, as shown in Fig. A. The inner strip is of brass, the outer 

 of steel. When the temperature rises the brass expands most and 

 straightens the coil, thereby deflecting the lever and pen, and so mark- 

 ing a graph on the rotating drum. 



Another form of thermograph is shown in B, which was placed 

 just at " Simpson's corner." The large brass bassoon and copper coil 

 were outside the hut in the " weather cupboard," while the small float 

 and drum were inside the hut. The air drawn into the bassoon by the 

 fan affected the volume of the alcohol in the copper tube, and so raised 

 or lowered the little float, and so actuated the pen. It needed to be 

 checked also by frequent comparisons. 



To determine wind velocity we had several instruments. On the 

 hill were the Robinson Cups, which whirled round merrily and were 

 registered by clockwork. Every six miles there was a signal sent 

 electrically to a chronograph inside the hut. Here we had a more 

 unusual instrument, called in full the Dines Pressure Tube Anemo- 

 meter, but early named the Blizzometer. Its records, owing to its 

 more sheltered position, were one quarter lower than those on Wind 

 Vane Hill. 



On the roof two vertical tubes were visible. One pointed into 





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