2'26 Mr. J. P. Joule on the Effects of Magnetism, 8^c, 



the tension as far as possible. I then found that the phaeno- 

 mena of elongation took place as in the case of the iron bars, 

 only to a smaller extent, which was obviously owing to the 

 degree of tension necessarily left in order to keep the wu-e ni 

 the axis of the coil. 



The new field of inquiry thus opened appeared to me to be 

 one of "reat importance, and calculated eventually to become 

 the means of throwing a great deal of light upon some of the 

 most interesting questions connected with molecular actions 

 and the real character of magnetism. I therefore constructed 

 an apparatus wherebv the effects of tension and pressure might 

 be further studied. This apparatus, which is represented by 

 the adjoining woodcut, consisted of a strong wooden lever A, 



Fig.]. 



furnished with a hard steel knife edge at K resting on a hard 

 steel plate. At the distance of one foot from the knife edge 

 a brass plate was fastened to the lever, into which a piece of 

 iron or steel wire, one-fourth of an inch in diameter, could be 

 screwed : the upper end of the wire could also be screwed 

 into a brass bolt, the head of which rested upon the cross 

 piece S. Weights coald be placed on the lever at W to in- 

 crease the tension. The magnetic balance, consisting ofa bar- 

 magnet eight inciies long, jjroperly furnished with scales, was 

 sitiiated at B. The further extremity of the lever was con- 

 nected with a fine lever multiplying eight times, the index of 



