1826.] Copper and other Substances during liotation. 'S^^ 



23*5 dwts. was very delicately suspended over it hf a fine brass 

 wire (No, 37), with a paper screen between the plate and the 

 disc. The distance between the surfaces of the plate and disc 

 tive-tenths of an inch. The plate being put in rapid rotation, 

 no sensible effect was produced on the disc. 



A bar magnet was placed on the screen under the disc : still 

 no effect produced by the rotation. 



A hght needle, weight 42*5 grains, six inches long, on a pivot 

 in a compass-box, being placed over the plate, the rotation 

 caused a deviation of 20° ; but when a heavy needle, weighing 

 197 grains, and of the same length, was similarly placed over 

 the plate, it immediately revolved rapidly with the plate. 



A bar-magnet, weighing 3 oz. 15 dwts. 19 grs. suspended by 

 a wire. No. 20, revolved rapidly with the plate. 



A horse-shoe magnet, weighing nearly a pound, and suspended 

 by the same wire, revolved with the disc. 



The following experiments were made with the view of ascer- 

 taining whether the effects increased nearly according to any 

 power of the decrease of the distance. 



A strong needle, six inches in length, weighing 197 grains, 

 and vibrating 22 times in a minute, delicately suspended on an 

 agate within a rim accurately graduated, was placed with its 

 centre exactly over that of the copper-plate, and being accurately 

 adjusted, so that the distance between the centre of the copper 

 and that of the needle was such as I required for the observa- 

 tion, the copper was made to revolve rapidly (always as nearly 

 as possible l2 times per second), and when the needle became 

 stationary, the direction of its south end (being that most con- 

 venient for observation) was noted. This was done with the 

 copper revolving in both directions, ''screw" and ** unscrew." 

 The direction of the south end of the needle was also observed 

 before the rotation. 



Distance, 



Screw. . . 

 Unscrew. 

 Mean. . . 



2-0 in. 



29° 40' W; Direction of south end 

 29 00 E S of the needle. 



20 



On diminishing the distance to 1*5 inch, the needle revolved 

 with the plate, and very shortly so rapidly, that it had the 

 appearance of an entire circle. 



After this I replaced the needle by others which were lighter, 

 letting every thing else remain the same, that is, the distance 

 Btill 1*5 inch. 



Needle weighing 42*5 grs. Needle weighing 25*5 grains. 



Screw 24° 40'W 10° 30'W 



Unscrew 25 20 E 10 40 E 



(I should mention that the needles were not at all neutralized). 



