290 



THE HEIGHT OF THE BARRIER AND THE SOUTH POLAR PLATEAU. 



The First Return Party left the main Polar Party at the Upper Glacier Depot and by 

 the time the Polar Party was at 3° Depot the First Return Party was on the Barrier in 

 80 54' S. The simultaneous observations give the difference in height between the Barrier 

 and 3° Depot as 9,198 feet ; while adding the three values for the stages we have 

 3,132+3,849+2,265=9,240 ; these two values agree better than might have been expected 

 their difference being only 48 feet, we therefore can take their mean 9,222 feet as being the 

 true difference in height between the Barrier and 3° Depot. 



Height of the South Pol.a.r Plateau between 3° Depot and 



THE South Pole. 



The changes of height on the plateau are relatively small and the method used above is 

 no longer applicable. The secular changes of pressure are now of the same order as the 

 changes of pressure due to change of height and therefore cannot be eliminated by the 

 changes of pressure at the base station which also is now nmch further away. The new 

 method was the following : The daily routine of the Polar Party was very regular, each day 

 the march occupied about 14 hours and the night rest 10 hours. The barometer was read 

 always, at the bsginning of the march, at the lunch camp and at the end of the march. Thus 

 before and at the end of each march the barometer was stationary for 10 hours. The change 

 in barometer during each of tbe periods of rest was determined and the mean rate of change 

 before and after each march calculated. This mean rate was then assumed to have remained 

 constant diiring the period of march and the observed difference of pressure corrected accordingly. 

 The following example will make the method clear : — 



Calculation of change in jpressure due to change in height during a march on the plateau. 



In this example we see that during the first night rest the barometer changed at the 

 rate of —-0022" per hour and during the second at the rate of —-0050" per hour. From 

 this we conclude that the barometer changed, due to pressure change, at the mean rate of 

 -■003G" per hour during the march. As the march lasted 14 hours the total barometer 

 change due to pressure change was —0036x14=— "05", while the actual observed change 

 was --16" thus leaving — •16+-05=--H" to be caused by change of height. A change of 

 -11" with a mean barometer of 20" and mean temperature of -13°F. gives a change of 

 height of 131 feet. 



