38 Mr. J. N. Hearder on the Atlantic Cable. 



two ends and flowing towards the centre to supply the gntta 

 percha with the electricity which the wire and battery have 

 extracted from it. 



Now it is quite evident that a second contact of the battery 

 with the wire whilst charged in either of the preceding conditions, 

 must be attended with results veiy diflerent from those of a 

 contact with a neutral wire. In the first case, viz. that in which 

 the two currents are flowing out of the wire, the second contact 

 of the plus or positive end of the battery will have to react against 

 the positive current flowing out in that direction, and cause it 

 it to return and flow out at the other end, and, following close 

 after it, will, when it reaches the remote end, merely produce 

 an effect equivalent to a continuous current without a break or an 

 interval between. If, on the other hand, the negative end of the 

 battery be brought in contact with the positively charged wire, 

 as in the case of a reversal, the efi'ect will be that its exhausting 

 influence will first facilitate the issue of the positive current from 

 the end of the wire with which it is brought in contact, and it 

 will then begin to extend its influence to the remote end of the 

 wire, following, as it were, upon the heels of the positive current 

 going out at that end, and calling back portions which might 

 otherwise have continued in that direction. 



With a negative charge in the wire, of coui'se the converse of 

 these actions takes place. So much time is occupied in the 

 transmission of a wave through the Atlantic Cable, that it is easy 

 to send a positive current in at one end, and, before it shall have 

 reached the other, to arrest it and cause it either to subside or 

 return, by reversing the connection, and substituting the negative 

 or exhausting end. I am using familiar terms, because these 

 remarks may meet the eyes of the unscientific as well as the 

 scientific, and I wish to be comprehended by both. It thus 

 appears that, whether consecutive currents of the same character 

 are sent forward, or reversals of the currents are employed, more 

 time is necessarily consumed than is commercially desirable, and 

 the value of the cable is hence considerably depreciated. 



I have alluded to the property of gutta percha to retain an 

 electric charge, known as its specific inductive capacity. This 

 property adds to the embarrassment ; for although gutta percha 

 takes up an electric charge very readily, yet that charge appears 

 to penetrate into its surface, and entangle itself in its pores, to 

 such an extent that it separates from it again with reluctance. 

 I have before drawn attention to an analogous property in crown 

 glass (Phil. Mag. April, 1858), which retains as much as 25 

 per cent, of the original charge, and parts with this residue with 

 great difficulty and in small portions at a time, so that, after a 

 coated plate of crown glass has been charged and discharged, it 



