Mr. Smiles, in his Life of George Stephenson, remarks:—“Sanitary objections were also urged in opposition to railways, and many wise doctors strongly inveighed against tunnels. Sir Anthony Carlisle insisted that “tunnels would expose healthy people to colds, catarrhs, and consumption.” The noise, the darkness, and the dangers of tunnel travelling were depicted in all their horrors. Worst of all, however, was ‘the destruction of the atmospheric air,’ as Dr. Lardner termed it. Elaborate calculations were made by that gentleman to prove that the provision of ventilating shafts would be altogether insufficient to prevent the dangers arising from the combustion of coke, producing carbonic acid gas, which in large quantities was fatal to life. He showed, for instance, that in the proposed Box tunnel, on the Great Western Railway, the passage of 100 tons would deposit about 3090 lbs. of noxious gases, incapable of supporting life! Here was an uncomfortable prospect of suffocation for passengers between London and Bristol. But steps were adopted to allay these formidable sources of terror. Solemn documents, in the form of certificates, were got up and published, signed by several of the most distinguished physicians of the day, attesting the perfect wholesomeness of tunnels, and the purity of the air in them. Perhaps they went further than was necessary in alleging, what certainly subsequent experience has not verified, that the atmosphere of the tunnel was ‘dry, of an agreeable temperature, and free from smell.’ Mr. Stephenson declared his conviction that a tunnel twenty miles long could be worked safely and without more danger to life than a railway in the open air; but, at the same time, he admits that tunnels were nuisances, which he endeavoured to avoid wherever practicable.”