Sig. Quirino Majorana on the Contact Theory. 253 



set up by the relative motion of different metals, I proceeded 

 to construct another piece of apparatus which is merely an 

 extension of the preceding one (fig. 2). In the new form 

 the electric current is obtained from the fixed armatures and 

 rendered continuous by a commutator carried on the axle of 

 the rotating armatures. 



Fig. 2. 



The rotating armatures form a series of ten disks, each of 

 which consists half of zinc and half of copper ; in the figure 

 all the zincs are above and all the coppers below. The fixed 

 armatures are carried by two insulating pillars and form 

 combs, each consisting of eleven half-disks of zinc or of copper 

 and all connected together. When the combs are placed in 

 position they allow the series of movable disks to rotate freely 

 between them without contact. 



The combs each carry a brush, which rests upon a metallic 

 ring mounted on ebonite on the revolving axle. The two 

 rings make contact each with one segment of a commutator, 

 the plane dividing the segments of which contains the lines 

 of junction of the two metals forming the rotating disks. 

 The binding-screws S and S' collect positive and negative 

 charges respectively, when the drum rotates in the direction 

 of the arrow. 



The greater intensity of current obtained from this appa- 

 ratus is entirely due to the greater total area of the plates. 

 The moving armatures have an aggregate area of 1327 

 sq. cms. of copper and the same amount of zinc. The distance 

 between the movable and the fixed armatures was about 2*5 

 mm. Hence if the apparatus makes 20 revolutions per second, 



