78 NOMOS. 



of rotation which has been founded upon their sup- 

 posed presence is tenable. That electrical currents 

 will cause rotation when passing at right angles to 

 each other has been abundantly demonstrated by 

 Ampere, and one of the instruments by which this 

 has been done is represented in the following 

 diagram. 



iiii 1 - : ; f 



Fig. 21. 



This instrument consists of two parts which are 

 essentially distinct from each other. The first part 

 comprises a copper ring-trough, a copper central pil- 

 lar, and a copper hoop. The trough and pillar are 

 fixed upon a flat stand, with the pillar in the centre. 

 The hoop, which is furnished with a cross-wire and 

 a pivot directed downwards, is detached. Belonging 

 also to this part are two binding-screws, the one 

 being connected with the trough, and the other with 

 the central pillar. In preparing for action, the elec- 

 trodes of a battery are connected with the binding- 

 screws, the trough is filled with dilute sulphuric acid, 

 and the hoop is placed with its pivot upon the central 

 pillar and its lower edge in light contact with the 



