1840.] The Galvanic Battery, 1159 



subjected to great strains, and were found most effective. The only 

 objection to the plan arose from the tendency of the thick wire to 

 break, and difficulty of reaching the fracture in consequence of the 

 strong adhesion of the insulating material to the wire. This of course 

 admits of being readily obviated by annealing the wire, or employing a 

 rope of small wires, instead of one thick one. 



Another method for making conductors for sub-aqueous explosions 

 [Fig. IV.] characterised by great simplicity, and possessing several im- 

 portant advantages, has been suggested by Dr. O'Shaughnessy. In this 



a. only one wire is insulated, by passing it through a series of corks, 

 which are subsequently coated with water-proof composition, and 

 wrapped round with wax cloth, or some other impervious substance. 



b. The second wire remains unprotected, and is simply tied with 

 twine to the corks. The chief objection to which, in practice, this plan 

 has been found subject, has arisen from the breaking of the corks across, 

 and the consequent exposure of the insulated wire to metallic contact 



c. with the other, or with adjoining substances. This objection 

 might be removed by serving the corks round with yarn, which, without 

 destroying the buoyancy they possess, would effectually remove the 

 danger of accidental contact, or by covering the wire with tape and 

 water- proof composition, prior to its being passed through the corks. 

 In all cases, however, in which charges are employed at great 

 depths, more perfect insulation than this plan affords would, it is con- 

 ceived, be essential. Under pressure, the corks become saturated 

 with water, and the consequence is that there is then no actual insula- 

 tion of the wire. To form a perfect conductor, the plan for entire 

 insulation ought therefore to be adapted for that portion of the wires 

 passing vertically downwards, and the corks should be used for the 

 horizontal portion ; lightness and buoyancy will thus be combined 

 with complete insulation of that part where insulation is essential, 

 and all risk of failure from accidental metallic contact, or diminution 

 of the heating power of the battery, avoided. 



The length of conductors is regulated by the limits of danger from 

 the effects of the explosions, beyond which it is essential to the securi- 

 ty of those engaged in the operations, that they should extend. This 

 limit will necessarily vary under varying circumstances, and cannot 

 always be determined with perfect accuracy. In blastjng rocks and 



