=Action of the Toepler-Holtz Machine.=--The action of the machine described above is best understood from the diagram of fig. 33. Suppose that a small + charge is originally placed on the inductor _CD_. Induction takes place in the metallic system consisting of the discs _l_ and _o_ and the rod _rs_, _l_ becoming negatively charged and _o_ positively charged. As the plate carrying _l_, _m_, _n_, _o_, _p_, _q_ rotates in the direction of the arrow the negative charge on _l_ is carried over to the position _m_, where a part of it passes over to the inductor _AB_, thus charging it negatively. When _l_ reaches the position _n_ the remainder of its charge, being repelled by the negative electricity which is now on _AB_, passes over into the Leyden jar _L_. When _l_ reaches the position _o_ it again becomes charged by induction, this time positively, and more strongly than at first, since now the negative charge on _AB_, as well as the positive charge on _CD_, is acting inductively upon the rod _rs_. When _l_ reaches the position _u_, a part of its now strong positive charge passes to _CD_, thus increasing the positive charge upon this inductor. In the position _v_ the remainder of the positive charge on _l_ passes over to _L′_. This completes the cycle for _l_. Thus as the rotation continues _AB_ and _CD_ acquire stronger and stronger charges, the inductive action upon _rs_ becomes more and more intense, and positive and negative charges are continuously imparted to _L′_ and _L_ until a discharge takes place between the knobs _R_ and _S_. There is usually sufficient charge on one of the inductors to start the machine, but in damp weather it will often be found necessary to apply a charge to one of the inductors by means of the ebonite or glass rod before the machine will work. =The Wimshurst Machine.=--The essential parts of an ordinary Wimshurst machine, as shown in fig. 34, are two insulating plates or drums. On each plate are fixed a large number of strips of conducting material, which are equal in size and are equally spaced--radially if on a plate, and circumferentially if on a drum. The plates, or drums, are made to rotate in opposite directions. The capacity of the inductors therefore varies from a maximum when each strip on one plate is facing a strip on the other, to a minimum when the conducting strips on each plate are facing blank or insulating portions of the other plate. There are three pairs of contact brushes, the members of two of the pairs being at opposite ends of diametrical conducting rods placed at right angles to one another; the third pair are insulated from one another and form the principal collectors, the one giving positive and the other negative electricity.