TO PHYSIOLOGICAL PHYSICS. [Chap. i. 



developed by induction. A and B are two plates of 

 glass distant three millimetres from one another ; 

 A is fixed, and B is movable on an axis revolved by 

 pulleys with great speed. In A are two oval windows, 

 at the extremities of the same diameter, represented 



Fig. 5. Holtz' Electrical Machine. 



unshaded in the figure. On the back of A, under the 

 window of one side, and above that of the other, is 

 pasted a piece of paper f f, called an armature, 

 from which a tongue of cardboard projects through the 

 window towards plate B. The glass plates, paper, and 

 tongues, are covered with a coating of shellac varnish. 



O ' O 



Opposite each armature, but separated from it by the 

 revolving plate B, is a row of brass points connected 

 with an insulated conductor. To work the machine 

 one armature is electrified by excited vulcanite or 



