324; Mr. Barlow's E.rpoiments on 



in fig. 7, and the lamp applied at E; a rotation immediately 

 commenced to the right, which soon increased to 30 revolu- 

 tions per minute. 



Ed']}. 18. The rectangle adjusted as before, and the lamp 

 applied at D, the rotation to the left, at the rate of 30 revo- 

 lutions per minute. 



E.vp. 19. We now suspended the compound rectangle, 

 fig. 8, and opposed to it the north end of the magnet, as in 

 fig. 9, and applied the lamp successively at E, D, G and F. 

 The following were the results : 



Lamp at E, rapid rotation to the right. 

 Lamp at D, rotation to the left, 30 per minute. 

 Lamp at G, rotation to the left, ditto. 

 Lamp at F, no tendency to rotation. 



Exp. 20. The magnet reversed, the lamp applied as before. 

 Lamp at E, rapid rotation to the left. 

 Lamp at D, rotation to the right, 30 per minute. 

 Lamp at G, no tendency to rotation. 

 Lamp at F, rotation to the right, 30 per minute. 



Exp. 21. The same experiments were i-epeated with two 

 magnets with contrary poles opposed, as shown in fig. 10. 



The results as above, but more rapid : in the last experi- 

 ments we obtained about 30 revolutions per minute, but it was 

 impossible to count them in these, when two strong magnets 

 were employed. 



It should be observed that in no case could any strong ten- 

 dency to rotation be observed when a magnet was employed for 

 a support, and the exterior magnet removed : fig. 1 7, in which 

 one branch is carried further from the magnet, showed the 

 greatest tendency. 



A pleasing exhibition of a compound motion of this kind is 

 shown in fig. 16, in which NS is a horse-shoe magnet with 

 an agate at each pole to rest the wire in, and L a lamp 

 which serves to heat each compound rectangle. The motion 

 in this case is not so rapid as in the former, but it is veiy 

 pleasing, and will continue as long as the lamp burns. 



Compound rectangles with six branches (fig. IS) were tried, 

 but there appeared to be little or nothing gained by this increase 

 of number. It appears, I think, that one with four branches 

 performs upon the whole the best. The length of the rect- 

 angles is about two inches, the depth an inch ; the diameter of 

 the platinum wire -y^jth of an inch, and that of the silver ^'yth ; 

 but it is by no means necessary to observe these dimensions. 

 In general it may be stated, that the lighter the I'ectangle, the 

 greater will be its velocity. 



Let us now endeavour to trace the theory of these motions. 



It 



