176 



PRESSURE. 



over the south of the Ross Sea than over the north. Wliether there is on the mean of the 

 year a depression over the Ross Sea with closed i.sobars must be left an open question. 



EAST LONa (70 



WCST LONG. if.o" 



Kio. .08. Pressure distribution year. 



Daily variation of pressure. 



It has already been explained how hourly values of pressure were obtained at Cape Evans 

 from the barographs corrected every four hours by means of the readings of the mercury 

 barometer. This series of observations extends from January 1911 to December 1912, i.e., 

 for 23 months. There are also available the two hourly readings of the barometer made 

 during 24 months, from February 1902 to January 1904, at Hut Point. 



The secular barometer changes are so great in McMurdo Sound, that a single month's 

 observations are practically useless for determining the true daily variation. It has therefore 

 been decided to give the data for each month separately in Volume III and to discuss here 

 only the final result obtained by combining the four years' observations for each month, which 

 give fairly regular and constant values for the daily variation. As only twc-hourly 

 barometer readings were made on the Discovery Expedition the nioan values for the fouj- 



