858 Memorandum of Experiments, tyc. QOct. 



over the mine — it therefore became necessary to contrive some self-acting 

 apparatus by means of which the requisite contact of the conductors 

 with the battery could be made at any desired period. 



Bearing in mind that all that is required to prevent the ignition of 

 the platinum wire is to cut, or otherwise interrupt, one of the conduc- 

 tors — or else to bring the wires into metallic contact with each other 

 between the battery and the platinum loop — it will be easy to under- 

 stand the action of the two pieces of apparatus which I now proceed to 

 describe. 



The first of these acts by restoring contact between the ends of a 

 divided conductor, thus completing the electric circuit and igniting 

 the wire. But as some unforeseen accident might interfere, and render 

 it necessary to examine the whole arrangement after the mine was laid, 

 a contrivance was added, which after an interval of four minutes 

 would break the circuit again and render every thing safe during exa- 

 mination. 



This apparatus is shewn at fig. 8. It consists of a watch from which 

 the minute hand was removed, and its place supplied by a strip of 

 copper four inches long and a quarter of an inch broad, and fixed by 

 its centre to the arbor of the minute hand. Each end of this index 

 carried by a thread a wire bent thus [)> the legs dipping into glass tubes 

 fixed in wood, and containing a portion of mercury. As the copper 

 index revolved, its advancing arm gradually lowered the bent wire 

 a a into the tubes, and thus established contact with the battery, one of 

 the conductors of which c, was interrupted at d and e. The opposite 

 arm, also connected with a bent wire b b, would lift this from a 

 similar pair of tubes after a lapse of four minutes, and thus break the 

 contact should no explosion have occurred. 



A glance at the figure in the plate will render the plan at once 

 intelligible. 



This apparatus could be set so as to go for any period from one to 

 thirteen minutes. The watch employed cost twenty-five rupees. 



The second self-acting contrivance was perhaps the simpler of the 

 two, and depended on the fact, that if the conductors come into metal- 

 lic contact with each other between the battery and the platinum 

 wire, the electricity does not reach the latter, and no ignition occurs, — 

 parting the conductors directs the electric fluid upon the platinum wire, 

 and ignition accordingly ensues. 



