TUNNKLLTNG THROUOH VARTOXIS STTiATA. 



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the loss of air owing to leakage in tlio portable tnbos, and 

 the constant damage and wear and tear to same, necessi- 

 tating also so many stoppages, more than counterbalances 

 any otlior advantages gained by their use, besides the often 

 reckless placing of the holes, and the unnecessary number 

 of them, both wasting labour and blasting powder. It 

 is not intended here to enter into any controversy as to 

 the relative merits of different kinds of drills, or of machine 

 and hand drilling, but merely as to the relative apparent 

 advantages, comparing time taken and the expense of dril- 

 ling. Time generally means money; and the cheapness of 

 hand labour may be more than counterbalanced by the loss 

 in time and the additional expense accruing from a work 

 being spread over a longer space of time. The author had 

 some experience a few years ago with the diamond drills 

 of the Diamond Rock-boring Company, who were the con- 

 tractors for a tunnel in South Wales. For heading driving 

 this is no doubt the quickest and most expensive system 

 of all, the amount of power required being very great, and 

 the loss in diamonds at times enormous, owing to their 

 tailing out of their sockets. This system is not suitable for 

 general boring, such as would bo required for enlarging to 

 the full size of the tunnel, owing to the cumbersome nature 

 of the machinery, and was not used for such in this case, 

 hut merely for driving the heading, which he does not 

 hesitate to say might have been driven for one-third or 

 probably one-half loss by hand labour. It is not intended 

 to disparage the diamond drill in its own particular pro- 

 vince of trial-boring, where it has no doubt done splendid 

 work, but merely to give an example of its use in an ordi- 

 nary tunnel heading. The machinery of the diamond, drill 

 IS very pretty. It consists of a small air oscillating engine 

 •attached to a standard, which is fixed on an iron trolly 



