NOMOS. 79 



sulphuric acid contained in the trough ; and when all 

 this is done the current may either pass to the trough, 

 thence through the acid to the hoop, and so back to 

 the other side of the battery, by way of the central 

 pillar, or else it may pass in a contrary direction. 

 This is one part of the instrument, and this is the 

 direction which the current pursues in it. The other 

 part of the instrument is a simple insulated copper- 

 wire, coiled several times around the outside of the 

 trough, and connected by its ends with the two 

 binding-screws to the right. These binding screws 

 are intended to receive the electrodes of a second 

 battery. The instrument is therefore arranged so 

 as to be open to two currents, and the current which 

 passes through the coil is made to cross at right 

 angles the current which traverses the hoop and 

 trough. This is the arrangement, and the result of the 

 arrangement is that the hoop is stationary when 

 either current is passed separately, and that it re- 

 'volves upon its pivot, to the right or to the left ac- 

 cording to the direction of the current, when both 

 currents are passed simultaneously. 



The curious phenomena of rotation of which we 

 have been speaking would therefore appear to be 

 due to the reaction of cross currents of electricity ; 

 and hence we may adduce a strong additional argu- 

 ment in favour of the idea that a magnet is sur- 

 rounded by electrical currents whose direction is 

 transverse to the line connecting the two poles. But 

 this is not all. On the contrary, there arise out of 

 the same premises many ulterior considerations which 

 are of vital importance in our present argument; 



