1168 The Galvanic Battery. [No. 108. 



when the depth exceeds sixty-five feet, a wrought iron cylinder will be 

 found necessary. 



For the priming apparatus, the following will, I conceive, be found 

 [Fig. XL] the safest, and most simple plan. The priming wires a. 

 must be inlaid in grooves on opposite sides of a circular rod of teak 

 wood, b. about I' 3" long, in the manner formerly described (when 

 detailing the experiments in Fort William) with sealing wax and 

 wedges, c. An iron tube, formed of a part of an old gun-barrel, 

 about r long, and having an iron flange 4'' square, carefully soldered 

 upon it d. at about three inches from one extremity, must be prepar- 

 ed, and into this the teak rod with its inlaid wires must be carefully 

 driven, till one end is flush with the exterior end of the tube, or that 

 nearest to the flange. Over this must then be laid a thick coating 

 e. of melted sealing wax, which both prevents the water forcing its 

 way through the pores of the wood, and also keeps the priming wires at 

 their points of issue from metallic contact with each other. The 

 interior extremities of the priming wires, / must then be connected 

 by the igniting platinum wire, which it has always, as far as my 

 experience goes, been found necessary to solder to the copper with 

 gold solder. A small cartridge of fine dry Dartford or mealed powder, 

 must then be placed in immediate contact with the platinum. The 

 apparatus might now be introduced into the cylinder, and by means 

 of the flange and screws, fixed there ; but it is of much importance 

 to have the means of insulating the priming from the main charge, 

 so that in the event of water penetrating to the one, it may not 

 communicate with the other, and it is also very desirable to have the 

 means of inserting and withdrawing the priming apparatus with 

 facility, so as to rectify any accidental derangement which may take 

 place, and these two objects are fully effected by the following plan, 

 g. due to Capt. Fitzgerald. A metallic protecting case is pro- 

 vided for the priming apparatus, and made a fixture within the 

 cylinder h. At its mouth a fine screw, at least an inch in length, is 

 made, and on the iron tube, immediately beneath the flange, there must 

 be cut a corresponding screw. By these means the priming apparatus 

 can be screwed in, or removed at pleasure. In finally fixing it in the 

 cylinder, washers of leather covered with white lead must be placed 

 beneath its flange, and the small fixing screws must be carefully 



