THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 



285 



values. Taking seasonal means, the highest 29'657 inches occurs in Spring, and the 

 lowest 29'572 in Autumn, the range being only 0'085 inch. 



Diurnal Range of Pressure. 



During the visit of the " Scotia," as already stated, a barograph was left at Cape 

 Pembroke, from which hourly values have been tabulated. The indications of this 

 instrument have been controlled bj^ the eye observations made six times daily, to which 

 the deduced values have been referred for the years 1903 and 1904, it having been 

 found that the mean pressure obtained from readings made at intervals of four hours is 

 exactly the same as that derived from hourlj^ observations. For the year 1905 the eye 

 readings made at 8 a.m. and 8 p.m. have been employed as a check. In order to get 

 the true mean, i.e. the mean of 24 hourlv readinsjs, the foUowinof corrections have been 

 used in dealing with the 1905 eye obsei'vations, viz. : — 



Aiu.'. Sept. Oct. 

 - -006 - -008 - •OOS 



Nov. 

 -•004 



Dec. 

 -•003 



Year. 



- •OOS inch. 



The following table shows the mean barometric pressure for the three years, corrected 

 to 32° and reduced to mean sea-level : — 



Mean Monthly Barometric Pressure. 



January 



February 



March 



April 



May 



June 



July 



August . 



September 



October 



November 



December 



Year 



Means: — Spring 29-636, Summer 29-562, Autumn 29-588, Winter 29-581 inches. 



It was found that the monthly differences between the Richard barograph and the 

 eye readings varied somewhat over the period ; and although the variation was small, for 

 the purposes of this investigation, which is to show the departure at each hour from the 

 mean of the day, it was considered desirable to take the monthly and seasonal means 

 from the above table of eye readings. In other words, the barograph values were used 

 differentially. 



