Submarine Telegraph Cables during Paying-out, 203 



difficulty should be considerably diminished in localizing small 

 faults. 



The balancing of the ship's battery on the shore-electrometer 

 by a similar battery stationed on shore, should be done either 

 with a set of ordinary resistance- coils, or, preferably, by a set of 

 Sir William Thomson's resistance-slides. 



The points for consideration are, that the battery which has 

 the highest potential should be bridged over with a resistance 

 sufficiently high, so that it may be impossible to produce any ap- 

 preciable alteration whilst the test is being applied*. The same 

 remark applies to the constant cells employed to balance the dis- 

 charge from the condenser used for the continuity-signals ; for 

 this purpose, too, it will be useful occasionally to take the con- 

 denser-tensions on the quadrant-electrometer with the resistance- 

 slide and constant cells in opposition. The insulation of the 

 condensers should be so perfect that no loss can be perceptible 

 during the time of making these tests ; and they should also, 

 on this account, be properly and completely charged, whether 

 from the cable or batteries. "When using the condensers with 

 the ship's electrometer for continuity-signals to ship, it is equally 

 important that they should be completely discharged. Any ten- 

 dency in the condensers to give too great residual discharges 

 should be carefully studied beforehand, and their effect on the 

 portable electrometer well noted. 



The constant cells used on the ship and on shore, and also 

 the electrometers, should all be very carefully compared by test- 

 ing against each other a short time before the paying-out 

 commences. 



The method here given for measuring the discharges from the 

 condenser will serve as an efficient test for comparing batteries ; 

 it involves, however, that their resistances should be ascertained. 

 A great advantage in favour of this plan is, that when the elec- 

 tromotive forces of the cells to be compared are nearly the same, 

 the resistances with which the stronger cell is bridged over will 

 be quite incapable of producing any alteration in its electromo- 

 tive force. 



Tamvvorth House, 

 Mitcham Common. 



* The battery on shore should contain a sufficient number of cells above 

 that on the ship, so as to be capable of being balanced against any increase 

 of tension from the ship's battery. 



