340 Mr. J. N. Hearder on a New Form of Telegraph Cable 



cause ; and I would now therefore direct attention to a new 

 form of cable, intended to reduce not only the amount of static 

 inductive action on the dielectric, but the degree of disturbance 

 produced by the residual static discharge. In order fully to 

 appreciate the value of this arrangement, it is necessary first to 

 consider certain electrical phsenomena resulting from peculiar 

 modifications in the arrangement of conductors and dielectrics, 

 which influence very materially the efifects of inductive action ; 

 I mean statical inductive action, commonly known as the charge 

 of the coating, in contradistinction to the dynamic inductive 

 action resulting from the influence of a current upon an adja- 

 cent wire. 



In all cases of the coated dielectrics, whether in the form of 

 Leyden jars, coated glass or other plates, or coated wires, there 

 are certain conditions which determine not only the amount of 

 charge which can be taken up by a given coated surface, but the 

 efibct which the discharge of that quantity can produce. A few 

 well-determined axioms, verified nearly thu-ty years since, will 

 serve as a guide in these considerations. 



1st. With any insulated charged conductor the statical in- 

 tensity or power of attraction exhibited by it will be as the 

 square of the quantity constituting the charge, and this holds 

 good whether the conductor be simply insulated in the atmo- 

 sphere, or form one of the coatings of a Leyden jar. 



2nd. The thermometric efi"ect of an electric charge, as ascer- 

 tained by a wire passing through the bulb of the thermo-electro- 

 meter, either as originally invented by Sir W. S. Harris, or as 

 subsequently modified by myself (see Phil. Mag. Nov. 1856), 

 is as the square of the quantity transmitted, other things being 

 the same. 



3rd. With a conducting or coated surface of a given area, the 

 length of spark or tension will be in the dii*ect ratio of the 

 charge. Thus, quantities of charge bearing the relations to 

 each other of 1, 2, 3, 4, will give tensions or length of spark, 

 as 1, 2, 3, 4 ; but the statical intensities as evidenced by attrac- 

 tion or inductive action, will be respectively in the proportions of 

 1, 4, 9, 16, &c., corresponding precisely to the thermometric 

 effect. 



4th. The relation of the quantity to the intensity will depend 

 upon the surface upon which the electricity is distributed : for 

 instance, a double surface charged to the same degree of tension, 

 that is to say, to give the same length of spark, will contain a 

 double quantity; but the statical intensity and inductive or 

 attractive action will remain the same, whilst the thermometric 

 eS"ect will be as the square of the surface or quantity, the thick- 

 ness of glass being equal. 



