Experiments and Inductions. 93 



gence until the other side is touched, when the leaves spring- 

 out with positive. Reversing again and bringing lower coating 

 near but not touching cap, faint positive is shown ; bringing it 

 down to touch, there is no divergence until upper coating is 

 touched, when the leaves spring out with negative. 



This may be repeated many times before the plate is dis- 

 charged. 



34. As these phenomena of the magic pane are fundamentally 

 characteristic of the electric force, and make their appearance in 

 uncoated non-conducting matter after excitement, it is well to 

 have a clear idea of their sequence. To assist in this I submit 

 the following method by diagram. 



Let n (fig. 11) be an element of a non-conducting surface ne- 

 gatively excited, andp an element of another non-conducting sur- 

 face positively excited. These surfaces may be in contact with- 

 out discharge or depolarization taking place. The polarized 

 condition is represented by the V lines, their aspect from p 

 towards n being male or entrant, and their aspect from n towards 

 p being female or recipient. When the surfaces are in contact, 

 the electricities are masked; their intensity is inappreciably 

 small. On separating these surfaces, mechanical force has to 

 be expended, and electric intensity is generated, or polarized 

 lines are spun having one root or extremity on the positive sur- 

 face and another on the negative surface. When the surfaces 

 are entirely separated, the electric excitement appears on both 

 sides of each excited surface, as at A and B of n (fig. 12), and 

 D and C of p. It is proper, therefore, to view an excited surface 

 as having two sides. 



In the following diagrams, surfaces that are excited are repre- 

 sented by thicker lines than those that are unexcited. 



Fig. 13 represents an element of the coated wax plate resting 

 upon the negative excited surface s of sulphur plate. The V 

 lines show the female aspect issuing on both sides of s. 



Fig. 14 represents the wax plate still resting on the sulphur, 

 but after having its top coating touched. This removes all the 

 V lines above x, which is now represented by a thick line, to 

 show that the top surface is now excited or charged; and the 

 aspect of the V in contact with x shows that the charge is posi- 

 tive or male ; but the charge is masked or engaged by part of 

 the opposite female force at s. Part of the force that issues from 

 s is free, and is directed in lines that proceed backwards from s, 

 and that turn round and, enclosing the engaged lines, appear in 

 front of x. This is proved from experiments 30. and 33. In 

 23. the force that acts inductively on the electroscope is positive, 

 which resides on the interior coating of the jar, so that its influ- 

 ence must radiate in a curved line to get at the electroscope. 



