president's address SECTION H. 169 



transmission can be raised to over 50 per cent., and, as this can be 

 accomplished with a reduced capital expenditiire, accompanied by 

 a more portable and easil\' erected plant capable of supplying the 

 power necessary for getting, hauling, pumping, and lighting, it 

 would appear that electricity is in the future destined to become 

 the principal transmitter for mining purposes. It is true that its 

 use in fiery pits cannot at present be regarded as absolutely safe ; 

 but enclosed motors, non-sparking switches, and Mr. Atkinson's 

 safety cable have greatly diminished risks which will, no doubt, 

 eventually be completely removed. 



The safety cable mentioned consists of a main and a subsidiary 

 conductor, in circuit with each being a fuse. These conductors are 

 connected with the same terminals at dynamo and motor, the 

 current dividing between them in proportion to their carrying 

 capacity. If now the main conductor be broken, the subsidiary 

 conductor remaininji intact, no spark results at the breaking, the 

 circuit still being closed, but the whole current is thrown on the 

 subsidiary conductor, and its fuse is melted, which occurrence, hy 

 means of a suitable mechanical arrangement, causes the whole 

 circuit to be switched off. To carry this principle into effect the 

 < able is composed of a closely wound spiral of tinned copper wire 

 (several wii'es being arranged in parallel), which is braided over 

 but not heavily insulated. Over this is laid a stranded conductor 

 of the required area, and the whole is then fully insulated. If the 

 cable be torn down by a fall, or broken in any wav by tension, the 

 inner conductor extends to an unlimited exten"- and maintains the 

 circuit until, by the action of the fuse, the whole cable is discon- 

 nected. 



Closely connected with mininfi are the tunnelling mn chines, which 

 have so lightened what was perhaps the most tedious work the 

 civil engineer could be called on to execute. The driving of the 

 Mersey and the trial borings for the proposed channel tunnel 

 marked a new era in such operations. An average forward progress 

 of ten yards in twenty-four hours, with a maximum of fourteen, 

 was obtained in the new red sandstone of the Mersey tunnel, whilst 

 the grey chalk of the channel was pierced at a maximum rate of 

 over a yard per hour, the heading in each case being 7ft. in 

 diameter. In extensions of the London underground railway the 

 needle system has proved expeditious and remarkably efficient in 

 preventing subsidence, there having been absolutely no disturbance 

 of the heavy buildings under the foundations of which the works 

 have been carried. 



The City and South London Railway, which, starting from the 

 Monument, traverses the bed of the Thames, and has its other 

 terminus at North Brixton, is carried for the whole of its length in 

 a pair of tunnels 10ft. 6in. in diameter, lined with cast-iron 

 segments. The heading was driven the full diameter of the 

 tunnel by means of a cutting shield forced forward by hydraulic 



