Read it through once

Still, he must take you as _far_ for fifteen cents as the other horse takes you for twenty-five. If he can’t do his fifteen-minute distance in fifteen minutes, he must still do the distance for the fifteen cents. Any stranger can check the distance off—by means of the most curious map I am acquainted with. It is issued by the city government and can be bought in any shop for a trifle. In it every street is sectioned off, like a string of long beads of different colours. Each long bead represents a minute’s travel, and when you have covered fifteen of the beads you have got your money’s worth. This map of Berlin is a gay-coloured maze, and looks like pictures of the circulation of the blood.