ELECTRIC GENERATORS. 123 



induction. In the Holtz it is derived from an external 

 source, begins 011 the stationary plate, and is then com- 

 municated to the revolving plate. In the Topler it is 

 produced by the machine itself, begins on the revolving 

 plate and is then communicated to the stationary plate. 

 In the Holtz it occurs on one side only. In the Topler it 

 is simultaneous on both sides. In the Holtz it ceases when 

 the plates are charged. In the Topler it is continuous. 



The absence of the brushes, carriers, and metal in- 

 ductors from the Holtz increases the internal resist- 

 ance, making it more difficult to charge, but giving 

 better insulation, and consequently greater energy than 

 a Topler of the same size. 



But the action of a Holtz is much more liable to 

 interruption from dampness, and a low electric poten- 

 tial in the atmosphere : since it receives only a small 

 initial charge, which is soon discontinued ; while that 

 of the Topler is constant, from the continuous action 

 of the carriers and brushes. So that a well constructed 

 Topler, with ordinary care, is reliable in any state of 

 the atmosphere, while a Holtz is very unreliable. 



COMPARISON BY DR. HOLTZ. In reply to an 

 inquiry as to whether the Topler machine was an 

 original, independent invention, or only a modification 

 of the Holtz, the author received a letter from Dr. 

 Holtz, written from Greifswald, Germany, March 20, 

 1883; in which he says, that his machine, as first de- 

 scribed in PoggendorfTs Annalen, in 1865 (volume 

 125, page 469, and volume 126, page 157), had "two 

 discs rotating in opposite directions, without stationary 

 discs " ; and that " The Topler machine, invented at the 

 same time, was a combination of two pairs of discs"; 

 two movable and two stationary. 



