SCIENCE AND PRACTICE. 411 



between the end a and earth, and c the end which is put to 

 earth ; then a perpendicular raised upon any point of the base 

 a c to the point of intersection with the hypothenuse b c will 

 express the electric tension or the charge at that point. The 

 superfices of the triangle a b c represents, therefore, the whole 

 charge held in the cable under these conditions. 



As a second case, suppose a battery of equal force to be 

 connected between the end c and earth, so that its current 

 circulates, in the same sense, in the line, as the battery 

 at a. The negative ordinate c d will then represent the ten- 

 sion of this battery and of the end c of the line ; and the 

 vertical distances between the straight line joining b and d 

 and the different points of the base a c will represent the 

 tensions in those points. The covered wire is, according to 

 this, from the end a to the middle e charged with positive 

 electricity, and from the middle to the end c with negative. 

 The whole charge of the cable is equal to the sum of the 

 opposite charges in the two equal triangles b a e and c d e, 

 or null. When the batteries have not equal tensions the 

 sum of the charges is positive or negative, according as the 

 stronger battery is connected with its positive or negative 

 pole to the cable. 



A third case of charge is when the end c of the cable is 

 insulated. The tension of the electricity in the point c will 

 then be the same as a b, and the charge of the whole cable 

 will be the contents of the rectangle a b X a c, which is 

 equal to twice the contents of the triangle a b c ; in other 

 words, the charge of every point of the cable will be the 

 same. 



105. Inductive Capacity of Materials. The amount of 

 this static charge depends, other things being equal, upon 

 the specific induction of the material with which the cylinder 

 is coated. 



Faraday says that the inductive action is communicated 

 from one coating of a jar to the other, from atom to atom, 

 through the dielectric. When the jar is a cylinder, there- 

 fore, the inductive action must be propagated, from atom, to 

 atom, in rings concentric with the conductor. 



