120 Rev. Mr Scoresby on the Uniform Penneahility 



The verifying of masonry or brickwork executed by contract, 

 and not sufficiently inspected, is another application of this 

 principle which might very often be useful, by enabling us, 

 without injury to the structure or finishing, however delicate, 

 to determine the thickness of almost every portion of the blank 

 walls with almost perfect accuracy. 



Mr George Stephenson, the talented engineer of the Liver- 

 pool and Manchester railway, suggested another application, 

 which, he conceived, might frequently be exceedingly useful in 

 the working of coal. In many cases it is the practice of the 

 colliers to run two parallel drifts through a great extent of 

 coal, leaving between them a wall, from 10 to 20 feet thick, 

 for the support of the roof, but which it is desirable should not 

 be thicker than necessary, to prevent the waste of labour and 

 coal. In this arrangement, which is often adopted when the 

 roof is loose, so as not easily to be supported, it is a matter of 

 great practical difficulty to prevent an undue encroachment upon 

 the limited thickness, that the safety of the roof be not endan- 

 gered. In such a case, the apparatus for the deviation might 

 be applied with much advantage, and the thickness verified, as 

 occasion might require. 



An engineer in extensive practice in Scotland, who recently 

 visited Liverpool, and happened to be present at the '' railway 

 area*" when I was trying the magnetic influence through a great 

 body of solid rock, expressed his exceeding delight in what he 

 witnessed, and mentioned several instances, in his experience, in 

 which the present process would have been of incalculable ad- 

 vantage. Two of the cases it may be satisfactory to mention. 



In an extensive colliery, with the general management and 

 working of which he was entrusted, a horizontal drift, designed 

 for carrying the water off the mine, by conveying it to the well 

 of the pumping-engine, was stopped up by the falling of a por- 

 tion of the roof. This circumstance, which completely put a 

 stop to the chief operations of the mine, occasioned them great 

 anxiety and perplexity, from their utter inability to determine 

 the extent of the fallen rock. Not knowing how small that ex- 

 tent might be, they did not dare to clear any part away below 

 the stoppage, lest the water should burst through and overwhelm 

 the workmen ; and to attempt to clear it from the upper^part, 



