On the whole, although opinions are divided in England, as to the use of shafts for ventilation after a tunnel is completed, it leans rather to the side, that unless in very long ones, shafts are of no use and had better be closed, as they are rather an interference with the natural current which difference of temperature, or prevailing winds, generally occasion; they also interfere with the great ventilating agency of quick trains. A tunnel is compared by many engineers to an _inclined_ chimney; and, as in the upright chimney, the draft would be impaired if there were several openings in its side, interfering with the direct currency of air for ventilation.
The Hauenstein Tunnel (already mentioned in our list of tunnels) is 2,731 yards long; it is straight throughout, and has a uniform gradient of 1 in 139. Three shafts were commenced in the construction of the tunnel—two only were completed, of which one, by a fearful accident through fire, that caused the death of between fifty and sixty persons, became irremediably choked up. The third shaft was used until the completion of the works, but it was closed immediately afterwards, and has not since been opened; the tunnel, therefore, is without ventilating shaft. We have, in the last three years, passed through this tunnel eight or nine times, and, notwithstanding the slowness of the pace, never experienced any inconvenience from want of effective ventilation. Mr. Storrow, who rode on the outside platform of the carriages (they are on the American plan), expresses the same opinion. The conductors of both the trains informed him that there is usually a current of air through the tunnels, and that the smoke disappeared in from fifteen to twenty minutes. Both complained of its being very wet from the dripping of water—a fact that we can fully confirm from personal experience.
Even with goods trains, drawn by two heavy locomotives, which burned coals, although the tunnel was filled with smoke, Mr. Storrow did not find respiration so difficult as what he had often experienced when sitting in a room with a smoky chimney; and he remarked on several subsequent trips the same day, how quickly the tunnel became free of smoke.