This was in the year 1879; and the story of the incident served to draw general attention to the discovery of a new and efficient means of transmitting power. Engineers recognised that in the steam-driven dynamo they had the means of producing powerful electric currents, while in the electric motor, connected by wires to the dynamo, they had the means of reproducing the power in mechanical form at a distance. There were, of course, losses of energy in the process. A certain percentage was lost in the dynamo itself, some in the transmitting wires, and some in the motor. But the all-round efficiency of the arrangement was much higher than that of any other system of transmitting power from one point to another several miles distant.
In order to apply this system to propelling vehicles it was only necessary to devise a continuous connection between the motor on the vehicle and the stationary dynamo. This was done on the first electric railway by means of a 'third rail,' substantially in the same way as is now familiar on underground and other electric lines. The third rail was a metal conductor supported on insulators and connected to the dynamo. The vehicle or car was furnished with a metal brush or skate which rubbed along the third rail as the car moved forward. The current thus collected was led through the motor (which drove the axle of the car through toothed wheels) and thence to the track rails, which conveyed the current back to the dynamo and so completed the electrical circuit. Messrs Siemens and Halske exhibited the first electric railway of this type at the Berlin Industrial Exhibition of 1879.
Another method of collecting the current was tried soon afterwards and formed the direct forerunner of the electric tramway on the now standard 'overhead' system. The disadvantage of the third rail system is that it involves an exposed 'live' conductor close to the ground. It is therefore quite unsuited for use on streets. Consequently the next step towards the electric tramway was to carry the electrical conductors overhead by supporting them on poles erected at the side of the track. The first installation of this kind was laid down at the Paris Exhibition of 1881. In that case the conductor was an iron tube with a slot along its lower side; and inside the tube was a 'boat' which slid along and was connected to the car by means of a flexible wire. A second tube, also with a boat and connecting wire, was provided to carry the return current. We shall see later how this arrangement evolved into the familiar 'trolley' system.
The mention of a slotted tube recalls the atmospheric system and, in so doing, emphasises the superiority of the electric system in simplicity, flexibility, reliability, and economy. Brunel's faith in the advantages of stationary engines and the transmission of power therefrom to moving trains would have been justified by the event if the pneumatic system of power transmission had been as practicable as the electric system. But there is an obvious contrast between the huge pipe of the atmospheric railway, with its impossible 'longitudinal valve,' and the small tube of the first overhead electric line or the third rail of the first electric railway. There is also a pathetic contrast between the prolonged struggles which Brunel and the inventors of the atmospheric system underwent before they were forced to acknowledge failure, and the rapid ease with which electric traction entered into its kingdom when the commercial dynamo and motor were first produced. The intrinsic difficulties which electric traction engineers had to meet were not serious. Designers passed, step by step, from the model electric railway at the Berlin Exhibition to public lines on a larger scale, and from the model electric overhead tramway to the 'street railway' or tramway which gradually supplanted the horse tramway. Each step consisted in an extension of the distance covered and an increase in the power required, coincident with a gradual improvement in the details of motors, dynamos, and transmission equipment.
CHAPTER IV
THE ESSENTIAL ADVANTAGES OF ELECTRIC TRACTION ON TRAMWAYS
A railway journal once committed itself to the statement that horse traction was superior to electric traction on roads because the horse possessed the 'vital principle' of energy in its constitution.
It is distinctly curious to find an authority on locomotion describing the essential drawback of horse traction as its distinguishing advantage. The 'vital principle,' unfortunately, needs food and rest to maintain it not only during working hours but during the hours of inactivity as well. In actual practice four horses out of every five in a tramway stud are in the stables while the fifth is at work. Moreover, the same stud has to be kept up, at a practically uniform cost, whether the daily traffic be light or heavy. Thirdly, the 'vital principle' has only a limited number of years during which—apart from sickness and disease—it is effective for traction purposes.