On a new Action of the Magnet on Electric Currents. 225 



a strong probability of at least one severe cyclone at each 

 minimum solar-spot period, and of its occurring in the same 

 year, or in the first or second year before the year of mini- 

 mum spots." 



[It is to be remarked that the three storms at the minimum 

 period of 1822 occurred in that year and the two years suc- 

 ceeding it.] 



Mr. Eliot proceeds : — " It will thus be seen that the con- 

 clusions to which I have arrived are quite different from those 

 established by Mr. Meldrum for the southern Indian Ocean. 

 His conclusions are that cyclones in that region are most 

 frequent and most intense at or near the maximum solar-spot 

 periods." Mr. Eliot considers that the data are too imperfect 

 to attempt to assign any reason for this opposite character of 

 cyclone distribution in the Bay of Bengal and the southern 

 Indian Ocean as referred to sun-spot periods. 



For the above views, we regard Mr. Eliot as an official 

 authority. We have read his memoir on the Madras Cyclone, 

 May 1877, with great interest, and consider that it embodies 

 very valuable information on cyclones generally. 



XXIX. On a new Action of the Magnet on Electric Currents. 

 By E. H. Hall, Fellow of the Johns Hopkins University*. 



SOMETIME during the last University year, while I was 

 reading Maxwell's ' Electricity and Magnetism ' in con- 

 nexion with Professor Rowland's lectures, my attention was 

 particularly attracted by the following passage in vol. ii. 

 p. 144: — 



"It must be carefully remembered, that the mechanical 

 force which urges a conductor carrying a current across the 

 lines of magnetic force, acts, not on the electric current, but 

 on the conductor which carries it. If the conductor be a 

 rotating disk or a fluid, it will move in obedience to this force ; 

 and this motion may or may not be accompanied with a 

 change of position of the electric current which it carries. 

 But if the current itself be free to choose any path through 

 a fixed solid conductor or a network of wires, then, when 

 a constant magnetic force is made to act on the system, 

 the path of the current through the conductors is not per- 

 manently altered, but after certain transient phenomena, 

 called induction-currents, have subsided, the distribution of 

 the current will be found to be the same as if no magnetic 

 force were in action. The only force which acts on electric 



* From a separate impression from the e American Journal of Mathe- 

 matics/ 1879, communicated by the Author; 



