Prof. Dove on the Changes of Wind in a Cyclone. 469 



electrical machine had been thrown upon the plate which did 

 not communicate directly with the ground, and the communica- 

 tion with the galvanometer had been established, the needle 

 deviated from 3° to 4° in one direction, and the same distance in 

 the opposite direction when the current of the spark was passed 

 through the water the other way. This deviation could be brought 

 to 15° or more by throwing several sparks instead of one upon 

 one of the plates, or by connecting the plate for a very short 

 time with the conductor of the machine during the movement 

 of its plate. 



We fear that the importance of this letter will not be propor- 

 tional to its length ; if, however, its contents should seem to 

 you to be worthy of attention, we shall be happy to see it pub- 

 lished in any manner you think proper. 



We remain, Sir, &c., 



J. G. S. Van Breda. 



Haarlem, September 1854. W. M. LoGEMAN. 



LIX. On the Changes of Wind in a Cyclone. In a Letter from 

 Professor Dove of Berlin to Captain Washington, R.N.j 

 F.R.S. 



13 Ashley Place, Westminster, 

 Dear Sir, September 12, 1854. 



IN our conversation yesterday on the subject of cyclones, I 

 made the remark that too wide an extension was given to 

 the theory respecting them when all changes of wind in a par- 

 ticular direction were referred to them, whereas an essential 

 distinction ought to be made between those changes of wind 

 which are produced by the advance of a cyclone over the surface 

 of the earth, and those which are the necessary consequences of 

 the phsenomenon which I have called the law of deflection. Per- 

 mit me to express my meaning in rather more detail. 



When a cyclone is moving over the earth^s surface in any 

 direction, the place of observation may be in either of two cases. 

 The middle or centre of the cyclone may, in passing, be either 

 over it or on one side of it. In the first case, the place is in a 

 diameter ; and in the second case, it is in a chord of the rotatory 

 storm or cyclone. In both cases the observer sees the wind- 

 vane as a tangent of the cyclone ; only with the difference, that 

 if it is the centre of the storm which passes over him, two winds 

 from directly opposite directions succeeding each other are 

 separated by an interval of calm ; whereas if, instead of being 

 on the diameter, he is on a chord at some distance from the 

 centre, he experiences no such interval of lull, but finds in its 

 place a more or less prolonged time during which the wind veers 

 round. The direction in which it does so is always opposite on 



