30 Mr. Roicard, An Investigation into the Isobaric [April, 



By referring to tlie weather in the typical cyclone mentioned before, 

 we can form a very fair estimate of that which may be expected to 

 visit the different districts traversed by the cyclone. In the western 

 districts, as it approaches, thin cirro-strati will be seen, with a halo 

 round the moon, as the trough is approaching cumulo.strati will be 

 developed, and high cirri blown into threads from the south-east. 

 The wind will meanwhile back, or veer as the case may be, to the 

 east and south-east, going more to the south as the trough approaches. 

 As soon as the barometer begins to rise a few hazy showers may fall, 

 or else a dense fog form, when the wind freshening from the south, 

 will ultimately blow strong with a rising barometer and a hard, clear 

 sky. I think it must be confessed that the foregoing is a very 

 accurate description of the sequence of weather in Cape Town during 

 the passage of one of these cyclones. 



The heaviest rain would naturally fall over the north-eastern dis- 

 tricts. Thunderstorms are prevalent in the advancing left hand 

 quadrant, consequently the north-eastern districts with Natal would 

 be very subject to them during the summer months. Moreover, as 

 this is the wettest half of the cyclone, these same districts would have 

 their wet seasons during summer and autumn, and comparatively dry 

 seasons during the other two quarters. 



Now what are the real facts of the case ? According to Mr. Gamble's 

 rainfall means, the N.E. and Eastern Districts of the Colony, with 

 very few exceptions, have their wettest months during the summer, 

 while the west and S.W. districts have their driest months then. I 

 think this of itself proves the general track of summer cyclones. 



When a cyclone advances over the Colony from the N. or N.W. it 

 is usually checked in its onward career by the comparatively higher 

 pressure to the south of us, but as this higher pressure is merely the 

 *' Col" joining the two anti-cyclones, there is a great tendency for the 

 cyclone to develope a secondary in it, and we know from experience 

 that primaries and secondaries, aud often two or more cyclones, very 

 often coalesce to form one again ; the whole system very often in this 

 way passes through the " Col," and is lost in the south seas. A case 

 of this kind was experienced over Europe in June, 1882. On the 

 26th a "Col" lay to the east of England, joining two anti-cj^clones, 

 one north and the other south. A small secondary was near Aber- 

 deen, while the primary was advancing on the coast of Ireland. The 

 forecasts were issued on the assumption that the cyclones would 

 advance to the north and the "Col" remain intact, but by next 

 morning the two cyclones had coalesced and formed a single system, 

 which was passing between the two high pressure areas, over the exact 

 spot where the "Col" was the day before. I have heard doubts 

 expressed as to the possibility of a cyclone breaking through a bank 

 of higher pressure, but from experience this is often known to be the 

 case in Europe, and I see no reason to doubt the possibility of it here. 

 But very often the advancing cyclone is checked by this bank, and 

 either fills up and dies away, or else passes off to the east. The result 

 of this is what one would look upon as a contradiction. According 

 to the law of winds as the cyclone advances we would expect N.E. 

 winds in Natal, east winds round the coast, and S.E. winds at the 

 Cape, all changing to S. as the cyclone moved away to the eastward. 

 But if the " Col " happens to stretch across the Colony, so as to have 

 gradients for west winds at, say Cape St. Francis to Port Alfred, 



