The total length of London’s greatest tunnel, the Metropolitan Railway, from Bishop’s Road to Moorgate Street, is 23,616 feet, or 4½ miles, less 144 feet. Starting from Bishop’s Road, the measurements are as follows:—For 3,024 feet, or 96 feet less than five-eighths of a mile, there is tunnel, then an open space of 675 feet around the Edgware Road station. From there to King’s Cross, 2 miles and 496 feet, is tunnel; but in this distance there are three most effective means of ventilation: the first is at Baker Street Station, 2,640 feet, or exactly half a mile from the Edgware Road Station. The second is at Portland Road Station, 2,978 feet, or 338 feet more than half a mile, from Baker Street. Portland Road Station is the most open of all the four intermediate stations. The third is at Gower Street Station, 1,920 feet, or 60 feet more than three-eighths of a mile. From Gower Street to King’s Cross Station is the longest interval between two stations, 3,900 feet, or 60 feet less than three-quarters of a mile. The distance between the King’s Cross and the Farringdon Street Stations is 5,192 feet, or 88 feet less than a mile. In this distance there are two tunnels—if one of them may be so called, for it is only 220 feet long; the other is 2,170 feet, or 190 feet more than three-eighths of a mile. In the remaining 3,836 feet, or 124 feet less than three-quarters of a mile, there are two little tunnels, one 523 and one 91 feet. During the hours the sun is above the horizon, complete light is never absent in the 91 feet tunnel—the train is no sooner in it than it is out again; and in the longer one there is for a moment or so “a dim religious light,” and then it is actual daylight. The amount of this, however, must depend upon the season of the year at which the passenger goes through it. In certain dark days of November it is hard to say which is the darker of the two—the tunnel or the daylight. The foregoing measurements will be readily understood by reference to the diagram herewith appended. It is a section of the Metropolitan Railway from end to end. As regards its ventilation we shall speak presently. [Illustration: SECTION OF THE METROPOLITAN RAILWAY. LONDON. _Horizontal Scale_ 2000 ft—1 _inch_ _Engineer, John Fewler, Esq._ _Vertical Scale_ 40 ft—1 _inch_ _General Manager, Myles Fenton, Esq._ ]