TRANSACTIONS OF THE SECTIONS. 35 
Dy. Ashe reviewed the known laws of cyclonal progress, their motion towards the 
8.W. in the southern, and the N.W. in the northern hemisphere while within the 
tropics, and remarked that in both cases this direction was nearly at right angles to 
the trade-wind of the hemisphere, and could not therefore be a motion due to the 
trade-wind, He noticed their recurving at the tropics, and subsequent course to 
8.E. in the southern and to N.H. in the northern hemisphere, and pointed out that 
since this occurred in the open sea as well as near land, it must depend on the 
latitude and some causal change connected therewith, and not on the proximity of 
land as some had supposed. He adduced Captain Fyers’s observations (Trans. Met. 
Soc. Mauritius, vol. iii. p. 29) as to the onward progress of cyclones being very slow 
at first on their formation near the equator, and increasing in rapidity afterwards, 
apparently part passu with their poleward motion. The author then pointed out 
that, in consequence of the difference in the rate of the earth’s diurnal rotation at 
different latitudes, air drawn into a cyclone from equatorwards would be moving 
more rapidly than the centre of the cyclone, and hence as it revolved round the 
centre in the eastern half would be discharging force into the mass of moving air, 
and thus accelerating its speed of revolution; while air drawn in from polewards, 
since it would be moving more slowly than the centre, would similarly use up the 
force of the western half, and so retard its speed of revolution. The same causes 
would also make the cyclone assume an elliptical, rather than a strictly circular 
figure, as usually supposed ; and the western half would present a greater excentri- 
city, on account of the greater differences of length in the degrees of longitude for 
equal intervals of latitude as we approach the pole; air from polewards would pass 
more to westward than air from equatorwards would to eastward ; hence the 
western half would have the larger surface, and would therefore experience more 
friction against the surface of the ocean than would the eastern. Both these effects 
would tend to produce the same result, namely, the comparatively slower revolution 
of the western half, a slower motion of the air composing it; this would cause the 
eastern half to roll over or past the western, and so produce a general onward 
progress of the cyclone in a direction parallel to a tangent to the extreme western 
point of the storm; that would, in fact, be along the minor axis of the ellipse, since 
such the author regarded it, formed by the storm, or, in short, in a poleward direction 
in both hemispheres. Some persons had supposed that the air in the western half 
of a cyclone would move the fastest because it moved along with the trade-wind, 
while that in the eastern half moved against it; but the author pointed out that 
this could only affect the rate of motion relatively to a ship at sea, and not as 
regarded the internal constitution of the cyclone, We should investigate the proper 
motion of the cyclone independently, and afterwards consider the entire cyclone as 
being carried on along with the trade-wind within which it was generated. The 
proper motion, then, the author considered to be to polewards in both hemispheres, 
or due south in the southern, and due north in the northern, though some easting 
might occasionally be due to a rapid poleward progress of the whole storm. To 
this proper motion the trade-wind component should now be added, or a N.W. 
progress in the southern hemisphere and a 8.W. in the northern. The resultant of 
these two, supposing them about equal in force, would give the actual intratropical 
path of the storm in each hemisphere, or W.N.W. in the northern and W.S.W. in 
the southern. ‘This was in exact agreement with the observed paths. At the 
tropics, the trade-wind failing, the proper poleward motion would alone remain ; 
this also was in agreement with observation. Beyond the tropics the storm would 
come under the influence of the 8.W. and N.W. counter-trades, and the resultant 
would be a N.N.E. path in the northern hemisphere and a §.8.E. in the southern; 
this also corresponded exactly with the results of observation. As the trade-winds 
increased in strength in the summer of each hemisphere the component of force 
due to their action would be greater, and a storm in the northern hemisphere would 
take a more southerly course, and in the southern hemisphere a more northerly 
course than at other seasons. This also was in accurate agreement with Captain 
Fyers’s observations of the storms of the South-Indian Ocean, since he finds (Trans. 
Met. Soc. Maur. vol. iii. p. 13) that “the November and December storms take a 
more southerly course than those of the succeeding months, January, February, and 
March.” After April the hurricane season as a rule is over in the South-Indian 
