Now, the undoubted
aim of all engineers is economy of construction and the securing of
permanent advantages. Mr. Crampton maintains that the suggested system
will give these, that three tunnels of, say, 17 ft. diameter, can be
constructed cheaper than one of 30 ft. diameter. After describing Sir J.
C. Hawkshaw's scheme for the ventilation of long tunnels, the three-way
scheme was discussed. Three separate tunnels of 17 ft. diameter each,
or 227 ft. area, are to be connected by large passages about midway
of their length. These passages are without valves; in fact, free air
passages. Between these midway connections and the ends, say again
midway between, is formed a branch at right angles either above or below
with separate openings from the branch into the other tunnels, such
openings being provided with doors or valves quite clear of the main
tunnel, any two of which may be closed, thus separating at this point
the corresponding tunnels from the third. The branch is to be led to any
convenient position where the exhustion apparatus can be placed.
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