The only solution of this difficulty seemed to be to pack the nickel in strong round tubes four inches long and about the size of a lead pencil, the sides of the tubes being finely perforated. But the expense of producing such tubes by ordinary methods was prohibitive. A machine was finally invented, however, which made the tubes economically by using spirally wound ribbons of metal, the edges being fastened together during the coiling process. By the use of these tubes the battery was so far perfected that it was given extensive trials in 1908 on electric vehicles; and as these tests proved satisfactory, Mr. Edison began the construction of a specially designed street car equipped with two 5-horse-power 110-volt motors of very light construction. The car weighs complete about five tons, and the batteries are stored under the seats running along each side.

This car was tested continuously for three weeks on one of the New York cross-town lines and performed its work so satisfactorily and economically that the management of the line decided to give the system a permanent trial. The regular daily run of this car averaged something over sixty-six miles, but this by no means exhausted the capacity of the batteries; and it is estimated that it could easily have run at least one-quarter farther without re-charging. The surprising feature of these tests was the low cost of running. The total cost of electric power for the day's run was about thirty cents, or 4.3 mills for each mile. The ordinary New York street car costs on an average about five cents per mile for electrical energy; but on the other hand, the carrying capacity of these cars is almost twice that of the Edison car.

The actual cost of running the car, however, was only one of its many advantages. The fact that no underground conduits have to be laid or overhead wires erected and maintained makes the initial cost of installing the line far less than by any other system. The reduction in the cost of maintenance of the line is also an important item, as it is estimated that the cost of repairs on conduit lines is about $15,000 annually per mile.

But the most convincing proof that Mr. Edison has really produced a practical storage battery car lies in the fact that, after testing his car for three weeks in actual traffic, the managers of the street-car line ordered sixteen similar cars for operation over their road.

MONORAIL SYSTEMS

The introduction of electricity facilitated the construction of monorail systems of roads, which had long been the dream of railroad constructors, since this power could be applied with so much more flexibility. The defects of the parallel rail system are apparent both in construction of the roadbed and the operating of trains. It is almost impossible to lay and maintain the rails in exact parallels, and even more difficult to keep each rail at the proper height at all points. Both these factors enter very largely into the determination of the speed that a train can make over such tracks, any very great variation from the parallel causing derailment, while slight depressions or elevations of either rail cause violent and dangerous rocking of the cars travelling at high speed.

In any monorail system the first of these difficulties, the deviation of the rail from the parallel, is, of course, eliminated; and it is found that on a single rail the elevations and depressions are not serious obstacles. Moreover, the cost of construction of a single-rail track must obviously be less than for a double-rail track, and the power necessary to operate cars over such a track far less. But until the invention of the gyrocar (which is referred to at length in the following chapter) the methods of balancing the car on a single rail presented difficulties which quite offset the advantages of the monorail system. Some of these methods are unique and a few of them are practical in actual operation.

In Germany a suspension monorail system is in operation, the cars being suspended from an overhead track. But obviously such a system, which requires elaborate and expensive steel trestle-work along every fork of the road, is not adapted to the use of long-distance roads except in thickly populated districts. A less expensive and highly satisfactory system is the one invented by Mr. Howard Hansel Tunis and used at the Jamestown Exhibition in 1907.

In this system the wheels, arranged in tandem, have double flanges which keep them on the single-rail track, and the cars are prevented from toppling over by overhead guides. These guides must be supported on a frame-work, but as there is little tendency to sway on a single-rail track, they can be relatively light structures. It is the cost of these frames, however, that practically offsets the low cost of road-bed construction, so that, everything considered, the mere matter of initial cost has no very great advantage over the ordinary double-rail road. But the cost of operating is considerably less than the older type, and this road would undoubtedly come rapidly into popularity but for the fact that such gyrocars as the ones invented in England and Germany are self-sustaining on the rail, doing away with the expensive overhead frame-work construction, and are likely to become practical factors in the problem of transportation.

In 1909 an electric aerial monorail up the Wetterhorn in the Alps was put into operation. On this line a car suspended on two cables, one above the other and without supports except at the upper and lower terminals, rises at an angle of forty-five degrees through a distance of 1,250 feet. There are two sets of these cables, each carrying a car so arranged as to work in alternate directions simultaneously, this counter-balancing effecting a great saving in power. The power-plant is located at the upper end of the ascent, and consists of winding drums actuated by electricity which raise and lower the cars by means of cables. On the cars themselves, therefore, there is no power, but each car is equipped with brakes powerful enough to stop and hold it notwithstanding the steepness of the incline.