481 



The diurnal variation, which is certainly very small, is nevertheless distinctly shown, and in each of the 

 four seasons it appears as practically a single oscillation with only slight modifications. 



In summer the total amplitude amounts to only 0-014 inch, with a minimum at al>out .'5 a.m. and a 

 maximum between 10 a.m. and 11 a.m., the afternoon decrease being slightly retarded between 5 p.m. and 

 9 p.m. The curve formed by the oscillation is, however, a very smooth one, and closely resembles in form 

 the curve of diurnal temperature variation for the same season. 



M. 



A.M. 



N. 



P.M. 



M. 



In. 

 01 



01 



00 



oo 



01 



01 



00 



Summer 



Winter 



Autumn 



faU o&sna.) 



(do.) 



(do) 



(do.) 



Equinoxes (Spr.vng f Autumn combined), 



I I | J I 



Fig. 2. Diurnal range of pressure (" Discovery "). 



The oscillation of greatest amplitude is that of the autumn, but even this does not amount to 02 inch. 

 The principal feature of this curve is the well-marked minimum at 5 a.m., followed by a quick recovery up 

 to 8 a.m., after whicli there follows a very gradual rise to the maximum twelve hours later. 



The winter oscillation is more irregular, but it, too, has a distinctly marked morning minimum at 6 a.m., 

 and evening maximum at 9 p.m., but the morning maximum, which is indicated more or less clearly in each 

 of the other curves, is most prominently shown here at 10 a.m., after which there follows a very small 

 afternoon minimum. 



3 Q 



