Section A. 



PRESIDENT'S ADDRESS. 



2.— THE DIURNAL VARIATION OF BAROMETRIC 



PRESSURE. 



By J. R. Sutton, M.A., F.R.Met.S. 



The present occasion is unique in my experience, inasmuch as it 

 is the first scientific meeting I have ever personally addressed. I have 

 contributed occasional papers to scientific societies, it is true, but in 

 every case I have had to depend upon some friend to read them for 

 me. You will see from this that the South African Association for 

 the Advancement of Science is scarcely to be congratulated upon 

 its President of Section A. If a moral may be drawn from the situa- 

 tion, it is that it is a mistake to expect every town which entertains 

 the Association to provide Presidents and Sectional Officers. You 

 would have got a President with more experience, and altogether 

 better suited to the position, by selecting officers on their merits, and 

 not on account of where they live. Any little inconvenience incurred 

 by appointing officers not in residence would be more than 

 counterbalanced by their suitability. 



Another reason for quarrelling with my position here is that I am 

 not qualified to pass in review, according to orthodox tradition, the 

 present state of the sciences comprised in this section. My topic has 

 necessarily to be special, confined to one branch of study ; if I were 

 to attempt more I should be speaking of things concerning which some 

 of my hearers would know more than I do. 



With this preface I have to ask for some forbearance and 

 attention while I bring before you some aspects of the fundamental 

 problem in Meteorology (one might almost say the fundamental 

 problem in Geo-Physics) : the semidiurnal oscillation of the 

 barometer. The case is this : All over the world, on land and sea, in 

 valleys and on mountains, the barometer rises and falls twice a day, 

 the maxima of pressure coming in general before Noon and before 

 midnight, the minima a few hours before sunrise and before sunset 

 respectively. It will be convenient to denote these in the following 

 way : — 



mi, the early morning minimum; 

 Ml, the morning maximum; 

 ni;, the afternoon minimum; and 

 M;, the evening maximum. 



