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conditions of work in each particular case. Where fuel is plen- 

 tiful and cheap, and where water-power is not available at a 

 coni]niratively reasonable cost, steam-power will nearly always 

 prove the more economical; where, however, the reverse con- 

 ditions exist, which is usually the case in a mountainous 

 country far from the coal regions, and inadequately supplied 

 with transportation facilities, but rich in mountain torrents, 

 water-power will generally be the more economical. In a suc- 

 ceeding chapter the power generating and transmission plants 

 for a number of rock tunnels are described, and here only a 

 general consideration of the subject will be presented. 



Steam-Power Plant. A steam-power plant for tunnel work 

 should be much the same as a similar plant elsewhere, except 

 that in designing it the temporary character of its work must 

 be taken into consideration. This circumstance of its tempo- 

 rary employment prompts the omission of all construction 

 except that necessary to the economical working of the plant 

 during the period when its operation is required. The power- 

 house, the foundations for the machinery, and the general con- 

 struction and arrangement, should be the least expensive which 

 will satisfy the requirements of economical and safe operation 

 for the time required. It will often be found more economical 

 as a whole to operate the machinery with some loss of economy 

 during the short time that it is in use than to go to much 

 greater expense to secure better economy from the machinery 

 by design and construction, which will be of no further use 

 after the tunnel is completed. The longer the plant is to be 

 required, the nearer the construction may economically approach 

 that of a permanent plant. As regards the machinery itself, 

 whose further usefulness is not limited by the duration of any 

 single piece of work, true economy always dictates the purchase 

 of the best quality. Speaking in a general way, a steam-power 

 plant for tunnel work comprises a boiler plant, a plant of air 

 compressors with their receivers, and an electric light dynamo. 

 When hydraulic transmission of power is employed, the air 



