Rear- Admiral FitzRoy on Meteorological Telegraphy. .399 



Buoys, and Beacons, Sir John Herschel stated that " the most im- 

 portant meteorological communication which could be telegraphed 

 would be information just fresh received by telegraph of a cyclone 

 actually in progress at a great distance, and working its way towards 

 the locality. There is no doubt that the progress of a cyclone may 

 be telegraphed, and might secure many a ship from danger by fore- 

 warning." 



Successive or rather consecutive gyrations, circuits, or cyclones 

 often affect one another, acting as temporary mutual checks, until a 

 combination and joint action occurs — their union causing even greater 

 effects, as may be seen even in water-currents, as well as in the 

 atmosphere. 



Between the tropics and the polar regions, or in temperate zones, 

 the main currents are incessantly active, while more or less antago- 

 nistic, from the causes above mentioned ; besides which, whenever 

 considerable changes of temperature, development of electricity, 

 heavy rain, or these in combination, cause temporary disturbance 

 of atmospheric equilibrium (or a much altered tension of air), these 

 grand agents of nature — the two great currents — speedily move by 

 the least -resisting lines to restore equilibrium, or fill the comparative 

 void. One current arrives probably or acts sooner than the other ; 

 but invariably collision occurs of some kind or degree, usually occa- 

 sioning a circuit, a cyclonic or ellipsonic gyration, however little 

 noticed when gentle or moderate in force. 



As there must be resistance to moving air (or conflicting currents) 

 to cause gyration, and as there are no such causes, on a large scale, 

 near the equator, there are no storms (except local squalls) in very 

 low latitudes. 



It is at some distance (from about five to twenty degrees) from the 

 equator that hurricanes are occasionally felt in their violence. 



They originate in or near those hot and densely-clouded spaces 

 sometimes spoken of as the " cloud-ring," where aggregated aqueous 

 vapour is at times condensed into heavy rain (partly with vivid 

 electrical action) and a comparative vacuum is suddenly caused, 

 towards which air rushes from all sides. That which arrives from a 

 higher latitude has a westwardly, that from a lower an eastwardly 

 tendency, due to the earth's rotation and to the change of latitude, 

 whence a chief cause of the cyclone's invariable rotation in one 

 direction, as above explained. 



The hurricane or cyclone is impelled to the west in low latitudes, 

 because the tendency of both currents there is to the westward along 

 the surface, although one, the tropical, is much less so, and becomes 

 actually easterly near the tropic, after which its equatorial centrifugal 

 force is more and more evident, while the westwardly tendency of the 

 polar current diminishes ; and therefore at that latitude hurricane 

 cyclones cease to move westward (recurve), go then eastwardly, and 

 toward the polar quarter. 



Great and important changes of weather and wind are preceded, 

 as well as accompanied, by notable alterations in the state of the 

 atmosphere. Such changes, being indicated at some places sooner 



