558 



Transactions. — Physics. 



Fig. 3 shows a short series of these waves with preceding 

 and following high pressures. Each vertical space represents 

 one day; each pressure-line represents r 2 oin. ; the small 

 arrows show the wind -movement, and the long feathered 

 arrow indicates the movement of all these pressures from west 

 to east. 



Wave-pressures (Southern Hemisphere). 



Ti#3. 



Using the same positions as in fig. 1, the rear or left- 

 hand side of the anticyclone is shown as now being indented 

 by the advancing depression D, and as this progresses east- 

 ward the wind at a changes to the north-west, pressure 

 continuing to decrease slowly until a little below 29-80, 

 when the wind comes from the west ; but at b the decrease 

 is to 29-60, also with north-west changing to west, while 

 at c pressure falls to 29-35 with the same wind-movement. 

 As Dpasses to the right or eastward pressure increases with 

 wind from the south-west at all three stations — a to 30 in., 

 b to 29-80, c to about 29-65. This change of wind— i.e., back 

 to west from the south-west, or from left to right — is the re- 

 verse of that which precedes it, and, as E is now approaching, 

 this backing movement is continued further towards the north 

 at each position ; it causes a second decrease of pressure which 

 at a falls to about 29-70, at b to about 29-45, and at c to 

 about 29-10. The wind-movement has now been from right 

 to left at all three places, and south-west winds with rising 

 pressure occur again as E continues its easterly movement, 

 the change at a being an increase to about 30, showing that 

 this place is now within anticyclonic pressure ; but b and c 

 remain within low-pressure limits, the increase being at 

 b to 29-90, c to 29-80, with the wind back again to west. 

 The approach of F causes pressure to decrease again with 



