‘ 
78 STORMS ON THE COAST OF NEW SOUTH WALES. 
exist between two places sufficient to produce gales, but before 
the air can be set in motion the wave of pressure passes on and 
removes the tendency to motion; and itis difficult in the ordiary 
atmospheric waves which pass over us to make allowances for this 
fact. At times when the wave is coming from the south a fresh 
breeze comes with it, but more frequently it passes with no 
appreciable effect upon our winds. Another difficulty is to esti- 
mate the effect of changing pressure at two stations, because it is 
impossible to tell how far the changes are going; a good illustra- 
tion of this will be found in the “ Dandenong” gale, of which more 
ere and rising to south, a gale was inevitable, and warning 
might have been given had a system for such warnings been mM 
been anticipated ; the change in pressure was so rapid that the 
effect was like an impulse that doubled the velocity of the wind 
suddenly. ~ 
_ Another term which requires defining before I make use of it, 
is cyclone. By it I simply mean currents of wind moving ma 
generally circular direction, and whirlwind would bea better 
term, were it not that we generally confine it to cyclones of such 
8. 
small dimension 
Two other words I should like to define, and then pass on to 
our subject: they are tropical and polar. By tropical currents 
or winds, I understand warm winds coming from any direction 
comes to a higher latitude 
tendency is so much greater than the earth’s surface motion 
west and north, or from south-east. But the tropical wind being 
“by far the more abundant of the two, when meeting the po 
wind generally deflects it, by the friction it exerts at the place of 
meeting, from its true course, and makes a south wind of it, an 
qual, veering to north as the tropical 
‘as the polar element increases, and 
= 
