The difficulties which had to be overcome in this great work were enormous, but there has been no break in the thread of progress. The 'tubes' are paying dividends which, though modest, are an encouragement to further developments. The finance of the District Railway has lost its element of chronic despair. Considered as a whole, the results prove that where there is the potentiality of large traffic, electricity is the instrument which must be applied. During the steam days, the most crowded part of the District Railway (the 'Inner Circle') carried a maximum of 16 trains per hour. With electric traction that figure has been raised to 40 trains per hour. And the remarkable thing is that with each increase in the service the traffic grows. Many people welcomed the electrification of the District as a measure of relief from the overcrowding on the steam trains during the busy hours. But with a service of trains more than doubled in frequency and also increased in capacity per train, overcrowding continues and the 'straphanger' has become an established institution. It may be accepted as substantially proved that, on suburban and inter-urban railways in populous districts, electric traction is a means of increasing traffic and diminishing the proportion of working costs. Moreover, these results have been achieved in conjunction with substantial reductions in fares and with marked improvements in the comfort of travelling. The engineering aspect of these changes has now to be considered. CHAPTER XIII ELECTRIC RAILWAYS FROM THE ENGINEERING POINT OF VIEW When electric railways were first considered, the natural tendency of engineers was to follow the existing model and merely substitute electric locomotives for steam locomotives. In point of fact, however, the engineering method now adopted is an evolution from the tramway model, not from that of the typical railway. A certain advantage was, of course, to be gained by replacing steam locomotives by electric ones. The greater 'starting torque' of the electric locomotive enables it to get a train up to full speed more quickly; and the capacity of the electric motor for taking heavy overloads assists the electric train in surmounting heavy gradients. Some advantage was also gained by producing all the power at a central source, instead of having a large number of steam locomotives, which are really power stations on wheels. But the electric locomotive had still to be made heavy enough to get sufficient grip of the rails; it had to haul its own dead weight; and it had to be made powerful enough to tackle a full-sized train on the steepest gradient with its complement of passengers, although the general demand upon it might be considerably less than that maximum.