Sept. 9, 1875] 



NATURE 



401 



from were the idea that there ought to be something 

 regular in the progress of hurricanes, and the observed 

 fact that in every disastrous storm the wind appeared to 

 move in a circle. They said to themselves : " We do not 

 seek to know how storms are formed, but how they pro- 

 gress." Instead of speculating, as did former meteoro- 

 logists, on storms of aspiration, on the role of electricity, 

 on the conflict of opposing currents, &c., they collected 

 for each tempest extracts from the log-books of all the 

 ships which had been involved in it. After having 

 abstracted and arranged this immense quantity of ma- 

 terial, they marked upon a chart, at certain dates, the 

 positions of these ships and the direction of the winds 

 observed. Then, by placing on this chart, after several 

 trials, a series of tissue-papers on which had been drawn 

 concentric circles, they made sure that the wind-arrows at 

 the same instant closely coincided with these circles, so that 

 at that very instant, over all the region subjected to the 

 storm, the mass of air resting on the ground or on the sea 

 must have been acted on by a vast gyrating movement 

 around a centre. Some idea of the nature of these re- 

 searches will be obtained from Fig. i, which shows a very 

 small part of the chart of the hurricane which ravaged the 

 island of Cuba in 1844. Redfield collected sufficient 



information to determine the figure of the hurricane at 

 twenty-five different times, between Oct. 4 and 7 ; the figure 

 shows two of these. The same phenomenon was repro- 

 duced at all the other times ; everywhere the hurricane 

 assumed this strikingly circular form. 



All tornadoes, typhoons, hurricanes, present the same 

 character wherever they occur, and they preserve it 

 throughout the entire duration, and over all their area, 

 which often extends to more than 600 leagues. The con- 

 clusion is evident ; there is evidence here of a vast rota- 

 tory movement, definitively confined to one portion of 

 our atmosphere, which is at the same time subjected to a 

 movement of translation. 



It is remarkable that when all the separate results 

 obtained over the whole of the northern hemisphere are 

 compared, it is seen that the gyration takes place always 

 and everywhere from right to left, in a direction opposite 

 to that of the hands of a watch (see Fig. i). Still more 

 remarkable is it that over all the southern hemisphere the 

 same law, the same gyration is found, but in a direction 

 opposite to that of the preceding, from left to right, i.e., 

 the same direction as that of the hands of a watch. There 

 is here evidently one law, and that a law without excep- 

 tion ; these terrible gyratory movements turn constantly 



Fig. I.— Hurricane at Cuba from Oct. 5 to 7, 1844. 



to the left in the northern hemisphere, to the right in the 

 southern hemisphere. 



Finally, the trajectories present some very striking 

 common characteristics in each hemisphere, and in both 

 hemispheres a remarkable symmetry. The lines tracked 

 by the centres of these cyclones do not descend directly 

 from the equator to either pole ; on the contrary, they 

 incline first to the west, then, after having passed the limit 

 of the trade-winds, they bend towards the east, in a 

 final direction roughly perpendicular to the former. Fig. 2 

 will enable the reader to follow in the two hemispheres 

 the development of cyclones. Originating not far from 

 the zone of calms or of variable winds, on both sides of 

 the equatorial zone, they measure scarcely more than two 

 or three degrees at the outset, but as they proceed towards 

 higher latitudes their area gradually enlarges. In the 

 two temperate zones they attain a diameter of more than 

 ten degrees, and frequently occupy upon the terrestrial 

 globe a space considerably larger than that of France. 



Thus all is symmetrical on each side of the equator, or 

 rather of the zone of calms, which oscillates a little each 

 year with the course of the sun. There is symmetry in 

 the direction of rotation, symmetry in the direction of 

 progressive motion, general symmetry in the figure of all 

 these trajectories ; and this holds good all over the globe. 



Such are the storm laws, the discovery of which is 

 mainly due to England and the United States, " the two 



greatest maritime powers of the world." The product 

 purely of observation, of empiricism, to use that word in 

 its highest sense, they have not yet reached the stage of 

 theory. On the contrary, in order to discover these laws, it 

 has been necessary to cast aside contemporary prejudices 

 and doctrines, the deadening influence of which we have 

 hourly opportunities of witnessing. 



Practical Rules.— ^vX the practical object of these 

 investigations is to save human life. Do we know of no 

 premonitory signs ? After the cyclone has commenced, 

 have we any means of discovering the direction of the 

 centre where the rotation is accelerated, where all the 

 sources of danger are accumulated ? How can we find 

 out the direction of its march ? How learn whether a 

 ship is caught in the dangerous region, where the rate of 

 the wind is the sum of the rates of rotation and of pro- 

 gress ; or in the moderate region, where the rate of the 

 wind is only the difference 1 Finally, what manoeuvres 

 are necessary in order to avoid the tornado or to escape 

 from it if by mischance we should be caught in it 1 



To all these questions there are answers, some exact, 

 imperative as are the exigencies of the danger ; others 

 more elastic, leaving room for tact and ability on the par 

 of a commander. 



By a fall continuous and prolonged, the barometer, 

 which is never at fault in the tropics, announces that a 

 cyclone is at a distance. As soon as the wind blows with 



