of all known Substances to the Magnetic Influence. 121 



where the water had risen within a yard of the roof, was a mat- 

 ter of much difficulty. Nor did the examination of the upper 

 part, by the engineer himself lying flat in a float, and pushing 

 himself forward by his hands against the roof, give him any sa- 

 tisfaction, further than this, that the portion of fallen rock being 

 solid, must be shaken with a blast, as affording the only means of 

 clearing away the obstruction. This hazardous experiment, after 

 much delay and anxiety, was at length undertaken and cleverly 

 accomplished; and, fortunately, the obstruction proving to be very 

 partial, the water made its way through the disrupted materials. 

 But it was a mere chance, as they knew nothing of the thick- 

 ness of the fallen masses. Had the thickness been many times 

 as great, they never could have ascertained how long it would 

 have been safe to have worked below the obstruction, nor when a 

 blast at the upper part would have been the most advantageous. 

 This, however, the magnetic deviation would have enabled them 

 readily to determine, and then they would have proceeded at 

 once to the most proper measures, and been relieved from the 

 greatest embarrassment. 



Another case which he mentioned was more important. In 

 the sinking of a coal-mine near the Frith of Forth, it was re- 

 quired, on one occasion, to run two parallel drifts or tunnels be- 

 neath this arm of the sea. It was essential, in this work, that 

 the two drifts should be near each other and parallel, but, for 

 the success of the future operations, they must not perforate the 

 separating wall. When, however, the tunnels had proceeded a 

 considerable distance, the workmen, misled by some mistake or 

 neglect on the part of the superintending miner, broke through 

 the septum, and the whole work, which had been conducted so 

 far at a great expense, was rendered entirely useless. Here, 

 then, was an instance in which magnets could have been em- 

 ployed with the greatest facility, and mu^t have been effectual 

 in preventing the accident which ruined the work. 



Though many more cases may easily be imagined in which 

 the process before us might be of important application, enough, 

 I trust, has been said to prove that it is not a mere matter of 

 philosophical curiosity, but is capable of becoming of extensive 

 and practical utility. 



