1826.] 



arising from its Rotation, 



113 



Direction of ro 

 tation of plate's 

 upper edge. 



e a, - 

 c g e: 



a> o es 



"^^^ 



•5 E.^ 

 <»- « .'■ 



2 d fl 





'fills 



WtoE 



00 04'W 



02 E 



02 E 



04W 



06 M^ 



08W 



EtoW 



20 50' E 

 2 50 

 2 46 

 2 44 

 2 42 



2 46 



1 22 



2 42 

 2 42 



Time of 

 observa- 

 tion. 



9'» 55™ 



10 05 



11 10 



20 35 



21 48 



22 01 

 22 17 



22 28 



22 40 



24 05 



25 36 



During this time the plate was kept per- 

 fectly stationary, and care was taken 

 that the apparatus should not be in the 

 least disturbed. 



After 21'' 48„, the plate was made to re- 

 volve slowly once from W to E. 

 After making the plate revolve several 



times and more rapidly. 

 Making the plate revolve several times 



from E to W. 

 Making the plate revolve once so slowly 



that the time of rotation was 3' 26". 

 The plate kept perfectly stationary since 



22" 40"*. 

 Making the plate revolve through 30* 



from W to E, and then bringing it 



back 30° from E to W. 

 Making the plate revolve through 90* 



from W to E, and then bringing it 



back90ofromEto W. 

 IMaking the plate revolve repeatedly and 



rapidly. 



<* From these investigations it appears, that the effect produced 

 on the iron by its rotation is permanent, so long as the plate 

 remains stationary : that it is independent of friction ; that it is 

 so far independent of velocity, that the iron can scarcely be 

 moved so slowly that the whole effect shall not be produced ; 

 and that the whole effect is produced by making it perform only 

 one fourth of a revolution. 



" Shortly after I had discovered these peculiar effects to be 

 produced by the rotation of iron, 1 pointed out the general 

 nature of the pheenomena, and exhibited some of them to 

 Mr. Barlow, and he has since made some experiments on the 

 rotation of spherical shells, in which he has found that phaeno- 

 niena somewhat analogous take place, but they appear to be 

 dependent on the velocity with which the shell is made to 

 revolve." 



" Since it appears, from all the observations which I have 

 detailed, that the direction of the magnetic polarity, which iron 

 acquires by rotation about an axis, whether it be at right angles 

 to the line of the dip, as would follow from the theory which I 

 have investigated, or not, has always reference to the direction 

 of the terrestrial magnetic forces, we must infer that this mag- 

 netism is communicated to it from the earth. It does not 

 therefore appear from this, that a body can become polarized 

 by rotation alone, independently of the action of another body : 

 so that if from these experiments we might be led to attribute 

 the magnetic polarity of the earth to its rotation, we must at 



New Series, vol. xiu i 



