32 Mr, Hoicardy An Investigation into the Isobaric [April, 



These storms must be generated on the southern edge of the 

 Atlantic anti-cyclone, somewhere to the west of us, and travel from 

 west to east. By referring to our typical cyclone we will be enabled 

 to judge the sort of weather which might be expected. 



The position and size of the Atlantic anti-cyclone will also affect the 

 path of these storms and cause them either to advance to us from \i 

 W.N.W. or a S.W. direction, from either of which points, or some- 

 where between them they always come. The position and size of the 

 Indian Ocean anti-cyclone will also govern the direction they leave us. 

 Numbers of these depressions come from the S.W., pass the Cape 

 from west to east, and leave us in a south-easterly direction, their 

 path being in the form of the arc of a circle. Others again come from 

 a W.N.W. direction, and pass by us towards the S.E. 



There is very little doubt that secondaries are of as common an 

 occurrence on the northern edges of these cyclones as they are on the 

 S.W. edges of the summer ones ; in fact I am of opinion that the 

 great majority of our winter weather is caused b}' these secondaries, 

 for in no other way can we account for the directions of the wind. 

 Captain Toinbee has proved that these South Sea depressions are of 

 enormous magnitudes, stretching from the South Coast of Africa to 

 the 70th parallel of south latitude, so that if our weather were merely 

 affected by these larger depressions, our winds would onty range fi-om 

 N.W., through W. to S.W., but very often the approach is heralded 

 by N.E. winds all round the coast, and the constant phenomenon of 

 the wind suddenly chopping from N. to W. as the trough passes, 

 points to the fact that the centre is not very far from us, and conse- 

 quently these depressions mu t be of small dimensions as compared 

 with the great South Sea cyclones, and must either be secondaries or 

 small independent storms generated, as I before said, on the southern 

 edge of the great South Atlantic anti-cyclone. 



But the question as to whether these storms be secondaries or not 

 does not affect our meteorology very much, because they are of such 

 dimensions as to bear all the characteristics of independent cyclones, 

 in ^\•h^ch light we can study them. Smaller secondaries are often 

 formed against the South Atlantic high pressure area, which 

 secondaries materially affect the Cape Peninsula, causing the wind to 

 blow from the N.W. when a S.W. wind would have been 

 prognosticated. 



An example of this may be seen in the storm which passed us from 

 the 21st to 24th of March this year. On the 21st the barometer was 

 steadily falling with a N.W. wind and all the atmospheric indications 

 of a winter storm. The predictions for Cape Town would have been 

 a sequence of N.AV., W., and S.W. winds. On the 22nd the wind 

 went more to the AV.N.AV., the indications increased, and a thunder- 

 storm broke over Piquetberg, with a few showers here. On the 23rd 

 the barometer had risen, but instead of the wind being S.W. it was 

 N., ultimately turning to N.W. and W. Heavy showers fell all day. 

 On the 24th the wind remained at W. till the afternoon, when it 

 backed to the N.W. again. Slight showers fell all day. Next day 

 the wind was S.W., and the barometer reached its maximum. By 

 studying the foregoing it is very evident that a secondary formed to 

 th« west of us, which altered the direction of the wind here on the 

 2;3rd and 24th. 



Tho30 socoudarios upset much of our forecasting if they are the 



