London is so large that it takes a long time to get from one end to the other, and the men who go down to the City for their work and come back every day want means of getting about cheaply and quickly. So there are omnibuses and trains and cabs in numbers. But the trains in London do not run above ground--there would be no room for them in the crowded streets; so there are railways in the earth, deep down beneath all the houses, and on them there are trains that run round in a circle. Those of you who have frequently been by the Underground Railway think nothing of it; to you it seems quite natural, for you are used to it. But it really is a most astonishing piece of work, as you would realize if you saw it for the first time. Just imagine how long it must have taken to cut out and carry away all the masses of earth that had to be removed to make a tunnel of such a length--a tunnel which should run right round underneath London. The most wonderful thing is that the houses under which it ran did not fall down and break through into it. But that has never happened, for the men who built the tunnel made it very strong, and lined it with bricks. And all day long, while people are walking about in the streets and horses are trotting in the daylight, down below the trains in the underground are running, running in the dark. It cannot be a very pleasant life to be an engine-driver on this railway: it must be almost like the life of a pitman who works down in the depths of the earth; yet the men themselves seem quite happy. The worst part of the railway used to be that as there are not many places where the smoke and steam can get out into the air, they hung in the tunnels and made the air very thick and bad, and there was, consequently, nearly always a sort of fog down there, and it was unpleasant to breathe the thick air; but all this has been remedied now, for the trains are run by electricity instead of steam. There are other underground railways in London also run by electricity, and they go through different districts, so by means of one or the other people can get near to almost any street where they want to go to visit their friends or to shop. In these, the fares are on the same system as on other railways: you pay for your ticket according to the distance you wish to go; but in the first one you paid twopence for all distances alike--twopence if you wanted to go right from the West End to the City, and twopence all the same if you were going to get out at the next station. Therefore some people nicknamed this railway 'The Twopenny Tube.'