450 Admiral Fitz-Roy [March 28, 



Gravitation ;* the grand results of both are exceedingly simple, but 

 the minor details become more and more complicated in proportion to 

 their minuteness/' * 



Consecutive storms, at the meetings of main currents, in zones of 

 latitude, at certain periods, have had appearances of continuity. The 

 familiar instance of the ' Cliarles Heddle * has so often been adduced as 

 proof of continuing circuitous action, or gyration, that it may seem 

 injudicious to doubt the evidence ; but knowing how frequently 

 circuits, or cyclones, succeed each other rapidli/ ; and how unreliable 

 are some of the earlier logs of events in a storm, written after its ces- 

 sation, especially respecting directions of wind and courses steered, 

 when waves and storm blasts were the guides, not the oscillating 

 compass (if indeed that had not been washed away, as in the * Charles 

 Heddle's ' case) ; it does not appear accordant to experience, and 

 enlarged acquaintance with the subject, to imagine that such atmo- 

 spheric eddies are, sui generis, erratic, and so considerably independent, 

 as to cross a wide ocean. 



When opposing currents meet, their masses must continue in 

 motion a certain time, either rotating, or ascending, or going onward 

 horizontally in combination. 



Masses of air, either of polar or tropical origin, so to speak, return- 

 ing, when driven back by stronger opposition, — at first, and for a 

 certain time, retain the characteristics of their peculiar and very 

 different natures. 



In our latitudes there is a continuous alternation of air currents — 

 each specifically different, and denoting approach by marked charac- 

 teristics : and we have proved by successive series of simultaneous 

 statical observations, over a wide range, — embracing Scotland, Ireland, 

 all Rngland, and adjacent islands, — that while these alternating or cir- 

 cuitously moving currents are thus incessantly passing — the whole body 

 of atmosphere filling our temperate zone is moving gradually towards 

 the east — at an average rate of about five geographical miles an hour. 



Daring strong westerly winds this eastward motion is greatly 

 increased ; and in easterly gales it is proportionally diminished, as 

 measured by its passage along a horizontal surface of earth or ocean. 

 Knowing these circumstances, and having accurate statical observations 

 of these various currents, at selected outlying stations, — showing 

 pressure (or tension), temperature, and relative dryness, with the 

 direction and estimated horizontal force of wind at each place simul- 

 taneously, the dynamical consequences are already measurable approxi- 

 mately, on geometrical principles ; and, judging by the past, there 

 appears to be reasonable ground for expectation that, soon, meteorolo- 

 gical dynamics will be subjected to mathematical analysis and accurate 

 formulas. The facts now weighed and measured mentally — in what 

 may be correctly called "forecasting" weather — are — the direction 

 and force of each air current, or wind — reported telegraphically to the 



* W. Stevenson, of Dunse, 1853. 



