166 ANNUAL OF SCIENTIFIC DIS'COVERY 



lated wire, with a conducting layer external to its insulating investment, 

 and turns up its further end into the air, and he then does the same thing 

 with a two hundred miles length of the same wire. He next communicates 

 as full a charge to each of these lengths as they have the capacity to retain. 

 Then he discharges each, allowing the discharge to flow through a fine wire 

 coiled round a bar of soft iron, so that the bar may be rendered a magnet 

 pro tern pore during the actual current of the electricity. Upon measuring 

 the force of each discharge-current, estimating it by the number of grains 

 the temporary magnet is able to lift, he finds that where the fifteen mile 

 length of the wire is concerned, the weight lifted amounts to 1,075 grains, 

 and that where the two hundred mile length is concerned, the weight lifted 

 amounts to 2,300 grains. A current which lifted 18,000 grains by simply 

 running through the apparatus thus arranged, upon being sent into a coated 

 insulated wire 498 miles long, lifted 60,000 grains when allowed to flow 

 back as discharge, and even 96,000 grains if the discharge passed from both 

 ends of the wire at once, and round the same temporary magnet. The sig- 

 nificance of this result, reduced to plain terms, is simply this the wires act 

 as reservoirs, and not as mere channels, and accordingly the larger reservoir re- 

 ceives and holds a larger quantity of the influence than the smaller one, and this 

 larger quantity naturally produces the most powerful effects when it is allowed to 

 escape from its imprisonment. If the wires were acting as common conduct- 

 ors, the longer wire would produce the weaker effect on account of the elec- 

 trical influence being attenuated through its extent. As they are operating 

 as Leyden jars, or reservoirs, the longer wire is the most capacious recepta- 

 cle, and produces the most energetic result, as its contents are poured out. 

 It is now a familiar fact, that sensitive magnetic needles, placed by the side 

 of a long and completely insulated wire when it is charged, give clear indi- 

 cation of the first " rush " of the influence into the wire, of the retention of 

 the charge for several minutes after the charging contact has been broken, 

 and of the final " rush out," or discharge of the influence in the opposite di- 

 rection, when the wire is connected with the earth by its nearer end. 



When the fact had been satisfactorily made out that the insulated marine 

 wire must act as a Leyden jar, and be affected by charge and discharge, it 

 became a matter of the highest practical importance to determine whether 

 there was any peculiarity in this mode of operation which might be expected 

 to interfere with the final success of telegraphy, in its application to long 

 distances of sea circuit. A length of 166 miles of cable chancing to be in 

 process of manufacture at Greenwich, the opportunity was seized to carry 

 practical research into the matter. This cable contained three very perfectly 

 insulated wires, arranged side by side in its core of gutta percha, in such a 

 manner that they could very easily be connected together by their ends, so 

 as to make an available length of wire for experiment of 498 miles. 



The first thing done with this arrangement was the experimenter's satis- 

 fying himself that he might use the results of his experiments as fair ex- 

 pressions of what would take place in an extended wire 498 miles long, not- 

 withstanding the three several wires, which formed successive parts of the 

 line, lying side by side in the narrow dimensions of the gutta percha core. 



