1164 The Galvanic Battery, [No. 108. 



this will readily be understood by a reference to Diagram No. 7, by 

 [Fig. VII.] which it will be seen that only two mercurial tubes, with one 

 bent wire, are employed. The wire c, c. suspended with its legs 

 dipping a little way into the tubes, is attached by means of a thin 

 metallic chain and hook to a loop of string (saturated either in saltpetre 

 or powder, so as to make it readily combustible) which passes through 

 the composition of a portfire a. from which, prior to its being fixed 

 in the wooden stand, part of the paper casing has been removed, as 

 shewn at h. h. This portfire burning down, ignites the combustible 

 string, and the bent wire falls by its own weight into the mercury, thus 

 completing the circuit. Should any accident delay the explosion, 

 then another portfire h, calculated to burn four or five minutes 

 longer than a. discharges a weight d. d. attached to it by means 

 of a loop of string, rendered combustible as before. This weight 

 on falling, raises the bent wire to which it is fixed by means of a 

 thin chain, completely out of the tubes, and thus effectually breaks the 

 circuit. On the first occasion on which this portfire stand was 

 employed, it was discovered that the composition of the portfire a. 

 just as it burnt out, fell into the tubes and checked the free action of 

 the apparatus, but this was immediately afterwards rectified by the 

 addition of a small copper plate e, for the portfire to rest upon, in the 

 centre of which an aperture was pierced, just large enough to admit of 

 the combustible string passing through. Throughout the very exten- 

 sive series of experiments, which was made to test the action of 

 the apparatus prior to its employment, on the occasion of the final 

 demolition of the " Equitable," no instance occurred in which the com- 

 position, even in the smallest quantity, fell into the mercurial tubes, and 

 this result was the more satisfactory, as some considered the above 

 defect fatal to the practical utility of the plan. Its susceptibility 

 of derangement was severely tested on the day of the explosion, as the 

 water was very rough, and the wind high, so that the boat in which the 

 apparatus was fixed, was continually coming in collision with the 

 neighbouring row-boats, and although large quantities of the solutions 

 of the batteries were thrown out in consequence, no part of the port- 

 fire stand was in the least degree disturbed, its subsequent action being 

 as complete as could have been wished. The expence of the portfire 

 stand is extremely trifling, as it may be made of any old materials 

 which may be available. 



