206 A. G. Hotvard. — The Wintei^ Stoi^ms of S. Africa^ [Sept. 28v 



high pressure. But supposing no such high pressure to exist, what 

 then ? And in any case it mast be confessed that the barometer i& 

 higher in front of a cyclone than it is nearer the centre, and conse- 

 quently the low must move to the high. If we assume that a low 

 cannot flow towards a high, then a cyclone must stand still unless the 

 high moves forward. But we very often see a high only giving way 

 when a cyclone forces it to do so, the result being some very stiff" 

 blowing, shewing that the high dies very hard. Moreover in a great 

 number of cases the cyclone splits the high into two and forms what is 

 now commonly called a " col " or neck. Hence the greatest energy 

 must be in the cyclone, and the initial motive power moving it from 

 west to east must be in itself. 



And what is this power ? Nothing more nor less than the 

 circulation of winds round the centre. 



Let us imagine a cyclone to be situated over the vSouth Atlantic ocean 

 to the west of us. The winds are blowing round the centre in the same 

 direction that the hands of a clock travel round the dial. But these 

 winds are of two kinds, one totally different from the other ; for whereas 

 the front Avind is an equatorial one, that at the rear is a polar one. 



The equatorial wind, or that which blows from the north is a warm 

 one, which causes the atmosphere to increase considerably in bulk for 

 an equal amount of pressure. Moreover this current is heavily charged 

 with moisture. But with the polar wind the converse is the case ; for 

 here though the pressure remains the same, the bulk will be much less. 

 We will now imagine two points at equal distances from the centre,- 

 one to the east and the other to the west. At both points the 

 barometer reads 30 inches, but there is a marked difference in the 

 atmospheric conditions of the two places, for whereas at the easterly 

 point the warm and rarified air extends to a great height, at the 

 westerly point the air being denser does not extend to such an altitude.^ 

 Thus the upper surface (so to speak) of the cyclone forms an angle 

 with the sea level, the line of which if extended to the west would 

 cut the sea at the spot where the cyclonic influence, ceases, but if 

 extended to the east would overlap the general surrounding atmosphere 

 and so complete the portion of the cone. It will thus be seen how my 

 figure of the inverted cone is borne out. 



From the foregoing it will have been perceived that for equal 

 pressure the air is much more rare on the advance side of the centre 

 than on the following. 



In fact the rarest portion is that in advance of the centre. The 



