70 Transactions. — Miscellaneous. 



straits or by the absence of anti-cyclones, or highs. These 

 arms sometimes appear to break off and form separate cyclones; 

 and sometimes a cyclone stopped by a high in front of it may 

 be overtaken by a succeeding cyclone, which coalesces with 

 it, and the increased energy thus obtained forces a passage 

 for the combined system. In summer the cyclones appear 

 generally on the south coast of Australia, farther to the east 

 than in winter ; they are less frequent, and travel somewhat 

 slower. In winter they appear usually as a depression off 

 Cape Leuwin, and they travel to New Zealand — about three 

 thousand miles — in from six to twelve days — in one instance 

 three days — or at the rate of about five hundred to two hun- 

 dred and fifty miles a day including stoppages, and they 

 succeed each other at the rate of about one in every six days. 

 In summer they travel at about four hundred to two hundred 

 miles a day, and they do not usually occur more frequently 

 than once in twenty days. 



"We can see a reason for this in the greater difference of 

 temperature during winter than in summer between the 

 equatorial and the polar regions, and the consequently more 

 rapid and vigorous circulation of air between them in winter 

 than in summer. 



To one other point I would draw attention, in conclusion. 

 We have seen that the great circulating systems of depres- 

 sion appear to travel from west to east, and sometimes with 

 great velocity. But the force of the wind does not appear to 

 be influenced by this eastward movement of the systems ; the 

 force of the wind depends apparently on the velocity of cir- 

 culation, not on the rate of translation. We must think, 

 therefore, that the eastward movement of translation, and the 

 corresponding movements north or south of these depressions, 

 are of the nature of wave-motions, not of horizontal motions 

 of the particles of the atmosphere. Such wave-motions are 

 not easily conceived, and they must be very complicated. Fresh 

 particles of the atmosphere are constantly being drawn into 

 the vortex and whirled upwards and outwards as the storm 

 moves on, and the force of the wind depends upon the vigour 

 of this circulation, not on the rate of its propagation. 



The whole subject is extremely difficult. The enormous 

 forces influencing winds and weather have been in operation 

 for thousands of thousands of years performing the beneficent 

 designs of the Creator, and men hitherto have known little or 

 nothing of the how. Within late years careful systematic 

 observation has given us some little insight into the modes of 

 operation, and I have no doubt that by degrees we shall learn 

 more perfectly the laws governing our weather, and be able 

 more accurately to forecast the immediate future ; and that 

 we shall understand better than we do now where and how 



