1840.] The Galvanic Battery. 1167 



sub-aqueous charges. The employment of the Galvanic Battery as 

 the igniting agent, removes, to a great extent, these objections, and 

 although, in sub-aqueous operations it is at present next to impossible 

 to foresee and provide against every source of failure, yet the probabi- 

 lities are now strongly in favour of success, whereas formerly they 

 inclined in the opposite direction. Every successive series of opera- 

 tions will furnish us with new information, and every failure of which the 

 cause is detected, will point out to us new precautions, so that in time 

 we may expect to see the arrangements for employing the battery so 

 fully matured in all their details, as to illuminate entirely those sources 

 of accident, which in the existing state of our practical acquaintance 

 with the subject, are so apt to escape undetected. 



An object of primary importance in all sub-aqueous explosions, is to 

 render the cylinder in which the charge is to be placed, perfectly water- 

 tight ; for, as Colonel Pasley remarks, " if there be even so much as a 

 pin hole to admit the water, it will inevitably reach the powder. The 

 material of which the cylinder must be made, will be determined 

 by the depth of water over it. For any depth less than 50 feet, 

 experience warrants me in stating, that a cylinder of wood, prepared 

 like a common cask, bound with iron hoops, having staves an inch 

 thick, and carefully coated exteriorly with sheet lead, will be found 

 effective. Such a cask or cylinder, five feet nine inches long, three ^eet 

 eight inches bulge diameter, and three feet three and a half inches end 

 diameter, was on one occasion of failure during the operations against 

 the " Equitable," left at the bottom of the river Hooghly, under a pres- 

 sure of fifty-one feet of water, for twenty-six hours, and on being raised 

 and immediately opened, it was found that the entire charge of 2050 

 lbs. of powder it contained, was as dry and serviceable as when it was 

 originally put in, and was in fact the identical powder with which, a 

 fortnight afterwards, the final demolition of the vessel was effected. 

 This may be considered sufficient to shew that within depths of fifty 

 feet, wooden cylinders cased with sheet lead, can with safety be employ- 

 ed. With a depth of ninety feet Colonel Pasley appears to have found it 

 necessary to have recourse to wrought iron cylinders, but the limit at 

 which the employment of wood becomes impracticable, has not yet 

 been ascertained. We must wait the results of other experiments ere 

 any decided opinions can be expressed ; but I am inclined to think that 



