1 18 Rev. Mr Scoresby on the Uniform Permeability 



In tunnelling, for instance, through rock, and working from 

 different shafts, this method of measuring the intermediate dis- 

 tance would often relieve the engineer from much anxiety, and 

 the miner from much personal risk, when the opposite workings 

 €ome near together. For although practical men, who have 

 been well experienced in mining operations, in tliat particular 

 kind of rock, may make a tolerable guess of the distance be- 

 tween the tw^o " head- ways " previous to their breaking 

 through, yet, it is well known, that very experienced engi- 

 neers have often estimated the interposed ri)ck at some yards in 

 thickness, when, in reality, it has not been more, than as many 

 feet. Blasting, under such a false supposition, it may be well 

 imagined, might be attended with the most fatal consequences. 



A very serious accident, that had well nigh proved fatal to 

 two very deserving men, happened in the working of the rail- 

 way tunnel under the town of Liverpool, which will very well 

 illustrate the present case. This tunnel, which is 2250 yards 

 in length, was excavated not only from the extremities, but also 

 from six or seven intermediate shafts. The person entrusted 

 with the superintendence of the working department, being a 

 practical man, was aware of their near approach to a junction, 

 and arranged a signal with the opposite party previous to their 

 making an intended blast. But the workman charged with this 

 duty, it would seem, did not believe that the junction was so 

 near, for whilst the confiding " overlooker,*" and a companion 

 on the opposite side, were listening to the sound of the picks, 

 the thoughtless miner, without giving the signal, applied the 

 match, when the force of the discharge, instead of re-acting, ex- 

 ploded forward about the defenceless heads of the unfortunate 

 individuals in the contiguous head-way. Most providentially, 

 they escaped with their lives ; but they were severely wounded, 

 their faces permanently blackened by the penetration of unex- 

 ploded gunpowder, and both of them suffered the loss of an 

 eye! 



In this instance, had the distance been accurately determined, 

 which it might have been by the magnetic influence to within a 

 quarter of an inch, they never would have attempted a blast un- 

 der such perilous circumstances, or at least no man would have 

 been so reckless of the safety of his fellow-workmen, as to have 

 made the discharge without a sufficient warning. 



