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



parts of the coil, which I have not time at present to describe. 

 Many more remain yet to be made. AYhen they are finished, I 

 shall prepare an account of them for publication in the Philoso- 

 phical Magazine. 



My object at present is, first, to show that iron wire, though far 

 inferior to copper in conducting power, is not unfit for second- 

 ary coils; secondly, to direct attention to the importance of 

 making induction coils so that with a given length, not of the 

 secondary wire, but of the coil, the longest sparks may be pro- 

 duced ; and thirdly, to show that a mere covering of the second- 

 ary wire with thread of any kind is not sufficient to insulate the 

 spirals of any layer from the adjoining ones of the same layer. 



MajTiooth College, April 4, 1859. 



LIII. On a Neio Form of Telegraph Cable intended to reduce the 

 effects of Inductive Action. By J. N. Hearder, Electrician, 

 Plymouth^. 



IN my last paper I described the nature of the inductive action 

 which takes place during the transmission of electrical cur- 

 rents through insulated submarine conductors, and pointed out 

 the various disturbing influences which it occasions. It is now 

 pretty well admitted by telegraph engineers, that, unless these 

 impediments to the free and rapid transmission of signals can 

 be either entirely removed or considerably lessened, the commer- 

 cial value of very long lines will be somewhat in the inverse ratio 

 of their lengths. As, however, the mechanical engineer has 

 overcome the difficulty of laying telegraph cables, it now remains 

 for the electrician to overcome the scientific difficulties which 

 beset his path, and to render his liue of communication tho- 

 roughly efficient after it is laid. 



Of late much attention has been directed to the subject, and 

 some verj' able communications from practical electricians have 

 contributed to throw much light upon it. From the very first 

 moment when the static charge of the gutta-percha coating was 

 bi'ought under my notice, I felt that it would one day act as a 

 formidable barrier to the extension of submarine lines ; and I 

 saw^ at that time no chance of remedy, except in the employment 

 of larger conductors and thicker insulating coatings. AVithin 

 the last year or two, plans have been proposed to reduce the 

 amount of induction, some of which appear to be founded upon 

 an incorrect apprehension of the electrical phfenomena to which 

 such arrangements would give rise. For instance, it has been 



* Read at the Plymouth Institution, March 3, 1859. Communicated 

 by the Author. 



