66 NOMOS. 



are arranged as in the diagram. The lower end 

 of the conductor is made to dip lightly into the 

 surface of the mercury ; the upper end is fixed 

 to a metal arm projecting from the summit of a 

 metal pillar whose base is in connexion with the 

 binding screw on the right. The magnet is made to 

 float vertically in the mercury contained in the glass 

 by a piece of thread which passes from its lower end 

 to a piece of wire which projects from the bottom of 

 the glass, the piece of thread being of sufficient 

 length to allow the upper end of the magnet to rise to 

 some distance above the surface of the mercury. The 

 wire to which the thread is attached is carried through 

 the foot of the glass to the binding screw on the 

 left. The instrument is connected with a galvanic 

 battery by means of the binding screws, and, when 

 the connexion is made, the current ascends the pillar, 

 traverses the arm, descends through the conductor 

 into the mercury, passes out of the mercury by the 

 wire which pierces the foot of the glass, and so out 

 by the binding screw to the battery again. The 

 current pursues this course or a reverse course, as 

 the case may be ; and as it does so, the free end of 

 the magnet is found to revolve around the lower end 

 of the conductor, to the right or to the left, accord- 

 ing to the direction of the current. 



Many instruments are also well calculated to show 

 the revolution of an electrical conductor 



The rotation - . . 



of an eiectri- around a magnet, but none is better cal- 



culated for the purpose than one which is 

 magnet. very like the last in form, and which is 



