In any event, however, the general introduction of the interlocking apparatus into the American railroad system may be regarded as a mere question of the value of land and concentration of traffic. So long as every road terminating in our larger cities indulges, at whatever unnecessary cost to its stockholders, in independent station buildings far removed from business centres, the train movement can most economically be conducted as it now is. The expense of the interlocking apparatus is avoided by the very simple process of incurring the many fold heavier expense of several station buildings and vast disconnected station grounds. If, however, in the city of Boston, for instance, the time should come when the financial and engineering audacity of the great English companies shall be imitated,--when some leading railroad company shall fix its central passenger station on Tremont street opposite the head of Court street, just as in London the South Eastern established itself on Cannon street, and then this company carrying its road from Pemberton Square by a tunnel under Beacon Hill and the State-house should at the crossing of the Charles radiate out so as to afford all other roads an access for their trains to the same terminal point, thus concentrating there the whole daily movement of that busy population which makes of Boston its daily counting-room and market-place,--then, when this is attempted, the time will have come for utilizing to its utmost capacity every available inch of space to render possible the incessant passage of trains. Then also will it at last be realized that it is far cheaper to use a costly and intricate apparatus which enables two companies to be run into one convenient station, than it is to build a separate station, even at an inconvenient point, to accommodate each company. CHAPTER XIX. THE WESTINGHOUSE BRAKE.