Contrasted with the tunnel of the Metropolitan Railway between Gower Street and King’s Cross Stations, where a sample of the air taken showed that CO was present to the extent of 25·9 parts per 10,000, the air of the tube railway is comparatively pure.” Dr. Parkes continues: “It may be safely asserted that constant travelling day after day, even if only for a limited period each day, in an atmosphere containing 15 to 20 parts per 10,000 of CO, such CO being derived solely from a human source, must eventually tend to injure health. There are two other dangers in tube-travelling which require notice. First, the danger in the warm summer and the cold winter months alike of bodily chill. In the hot weather the traveller passes suddenly from the warm street into a much colder atmosphere below the ground level. In the winter the reverse happens--the passenger who has been warmed and enervated by the devitalised air below meets the chilly wintry blast on emerging into the street. Secondly, the air of the tube being very dry, and constantly in movement, there must be much organic dust of human origin floating in it. The dangers of tubercular expectoration are no doubt intensified in such a dry and shifting atmosphere as that of the tube, and the cautionary notices to prevent spitting are wisely exhibited in every carriage.” On the whole, Dr. Parkes favours open air to other methods of travelling. He recommends that as far as possible travelling should be by routes open to the air of heaven. CHAPTER XX _SOME ELECTRIC LOCOMOTION DRAWBACKS (continued)_ TRAMWAY ACCIDENTS When the Chiswick High Road tram-line was being made the tradesmen petitioned the London County Council against it. They complained of the annoyance as well as of the danger of the trams. They said that the trams, being large (carrying seventy people in all) and running on eight wheels, made considerably more noise than the light horse-car; that the motor was not silent, and the progress of the trolley along the shivering overhead wire made a continuous, most unmusical, and penetrating din; while the brake--of necessity powerful--also had a harsh note quite its own. To this was added the noise and flash of electric sparks and a singularly sonorous and imperative bell in place of the usual whistle; and as the cars came along every two and a half minutes in each direction, they who dwelt along the route did not find them altogether lovely.