Even in the early days of street-railway construction the extravagance of the method of horse-power traction was fully appreciated, and the numerous improvements in steam-engines stimulated attempts to adapt the locomotive in some form to city railways. But there were many difficulties in the use of the ordinary, or specially constructed, locomotives in the crowded thoroughfares of the larger cities. It was practically impossible to eliminate their smoke; and their puffing and wheezing, which frightened horses, caused numerous accidents. But even if these defects could be corrected, the locomotive was known to be an expensive form of motive power, when applied to a single short car, carrying at most only a few passengers and making frequent stops, as was necessary in street-car traffic. The inventors, therefore, looked about for other methods of applying steam power. But it was not until 1873 that this idea took the practical form of the cable road, on which single cars could be operated by means of underground cables travelling in slotted tubes, and propelled from a stationary power-plant. The first practical cable system was made by Andrew S. Hallidie, and his associates, who planned and put into operation the first cable line in San Francisco. It proved to be entirely successful, and was imitated almost immediately in most of the larger cities of the United States, and in some European cities. Within a decade the number of cable railways installed had so reduced the number of horses necessary for operating street-car lines all over the country that there was an appreciable depression in the market prices of such horses. The importance of this method of transportation is shown in the fact that between the years 1873 and 1890 more than a thousand different patents directly connected with the operation of cable roads were issued by the United States Patent Office. But by 1890 electric traction had become practical, and the issuing of patents for cable lines ceased as abruptly as it had begun. Before the close of the century practically every important cable line in the United States had changed its motive power to electricity. Thus in a brief quarter of a century this method of street-car traction had come into existence, revolutionized all hitherto known methods, and become obsolete. EARLY SELF-CONTAINED SYSTEMS In most of the earlier attempts to solve the problem of electrical propulsion the motor vehicles were constructed on a self-contained plan--that is, the power was generated on the locomotive itself, just as in the case of the steam locomotive. As early as 1835 Thomas Davenport, a blacksmith of Brandon, Vermont, constructed such a motor operated by cells, and built a small circular railway in Springfield, Massachusetts, on which he drove this electro-magnetic engine. This miniature railroad was of no practical importance, but it has the distinction of being the pioneer electric road.