180 Prof. Challis on the Hydrodynamical Theory of the 



from the rotation of the earth is altogether inadmissible ; for 

 the hurricane always commences in very low latitudes, with a 

 diameter which seldom occupies more than 2 or 3 degrees of 

 the meridian. The difference in magnitude of the parallel 

 circles, however, is so inconsiderable that the air streaming to 

 the centre can only be deflected by the earth's rotation to an 

 angle of 2 or 3 degrees from the meridional direction. As- 

 suming that the centre of the cyclone is, at the beginning of the 

 hurricane, in 10° latitude, that its radius occupies 2 degrees of 

 the meridian, and that the air requires two hours in order to 

 traverse this distance, and retains during the whole time the 

 rotation-velocity of the parallel circle which it has left behind, 

 in this case the air-particles from the 12th degree of latitude, 

 streaming to the centre of the hurricane, would deviate a little 

 to the west from the meridian, forming with it an angle of 2° 45'. 

 Those from the 8th degree of latitude, streaming to the centre, 

 would deviate eastwards, their direction forming with the meri- 

 dian an angle of 2° 21'. But this much too small deviation 

 from the meridian cannot possibly occasion the rapid whirling 

 motion of the storm. 



Not doubting that such a theory of the ocean-currents and 

 the trade-winds, founded on the attraction of the moon, may be 

 the correct one, we nevertheless acknowledge how much our view 

 needs to be subjected to further elucidation. Time must bring 

 a multitude of fresh observations before the special authorities 

 can have spoken their last word on this subject. To us, how- 

 ever, it will afford the fullest satisfaction if we have had the 

 good fortune, by the foregoing analysis of our views, to contri- 

 bute, at least indirectly, to the advancement of this department 

 of physical geographv, which has hitherto wanted a uniting fun- 

 damental idea. 



XXIX. The Hydrodynamical Theory of the Action of a Galvanic 

 Coil on an external small Magnet. — Part I. By Professor 

 Challis, M.A.,F.R.S* 



1. PT HE mathematical theories of the physical forces which I 

 Jl have published from time to time in this Journal have 

 been made to rest exclusively on the following hypotheses : — All 

 visible and tangible substances consist of inert spherical atoms 

 of constant magnitude, and all physical force is either mode of 

 pressure of the sether on the surfaces of the atoms, or reaction 

 of the atoms at their surfaces due to the constancy of their form 

 and magnitude. The sether is supposed to be a continuous 

 elastic substance, filling all space not occupied by atoms, of 

 * Communicated by the Author 



