will eschew sensational science; a journal which, just as the London Times is regarded as the authority on political and economical questions, will be looked up to as an authority on matters of science.

In order, therefore, to protect the public against scientific bubbles we must impress upon both men and women the fact that an education in science is desirable, and is becoming more important as the world grows older; but until a scientific education becomes more general, it is important that there should be some scientific oracle of Delphos, and I can not think of any better than a well-managed scientific journal, the editors of which will seek for the best information on scientific questions which interest the financial world. When it is known that such a journal admits to its pages nothing that is sensational, when it is realized that the best specialists contribute to it, surely it will become a saving help in times of trouble.

WHAT MAKES THE TROLLEY CAR GO.
By WILLIAM BAXTER, Jr., C. E.

II.

If the successful operation of a street-railway car by mechanical power depended wholly upon the ability to produce a motor of sufficient capacity to do the work, the problem would be an easy one to solve, and would have been solved long before the advent of the electric motor. Mere ability to furnish the necessary power, however, is not enough to meet the requirements. As already shown, the mechanism must be light, strong, compact, simple, and so well protected that it can not be injured except under abnormal conditions. In addition, speed-controlling devices must be provided whereby the velocity may be changed at will and in the shortest possible time, and with as nearly absolute precision as possible. This controlling mechanism must also be so arranged that the direction of motion may be varied with the greatest certainty and as rapidly as may at any time be required. The way in which these results are accomplished in an electrically operated car can be understood from Figs. 18 and 19, which are line drawings, in a simplified form, of an ordinary trolley car. Fig. 18 is an elevation showing the outline of the car body and the wheels in broken lines, while the motors and the wires through which the current is conveyed thereto are drawn in solid lines. Fig. 19 is a plan in which the outline of the car floor and the platforms is represented in broken lines, the solid lines being the motors and connecting wires.

In almost every instance railway cars are provided with two motors, as shown at M M in these two figures. This arrangement is adopted not because one motor can not furnish all the power required, but simply for the purpose of making the equipment more reliable. Everything of human make is liable to fail; hence if only one motor were used there would be more or less liability of its giving out at a critical moment, and then the car would be helpless. If two motors are provided, should one give out the car would not be disabled, for the remaining machine would be able to run it to its destination. In order that this result may be successfully accomplished, each motor is made of sufficient capacity to run the car without being overtaxed, unless the load is abnormally large; but even under the latter conditions the machine will in ninety-nine cases out of a hundred withstand the strain. Some roads, in small towns, where the traffic is light and the expense must be kept down to the lowest point, use single-motor cars, so as to effect a saving in first cost. This course, however, is very seldom followed, except in places where there are no heavy grades or where there is very little probability of the loads becoming excessive, except at rare intervals. If the cars are provided with a single motor, when one becomes disabled from any cause it has to wait until overtaken by the car behind it, so that it may be pushed by the latter to the end of the road.

The electric current for operating the motors is generated in a power house that is located at some convenient point along the route. The current is conveyed to the moving cars by means of a trolley wire, which is marked T in the drawings. Unless the road is very small and operates but a few cars, this wire will not be sufficient to carry all the current, hence in most cases there are a number of supplementary wires, which are called feeders. These wires are carried along on poles, and at proper intervals are connected with the trolley wire T. The electric current passes from the trolley wire through the motors on the car, and thence to the rails R, and through these, and also through the ground, back to the power house. The exact path of the current is as follows:

Figs. 18, 19.—Outline Elevation and Plan of Electric Railway Car, showing Location of Motors, Controlling Switches, and Connecting Wires.

From the trolley wire, through the trolley pole t, to the fixture on top of the car which holds the latter. From this fixture, as shown by the heavy full line, the current passes to a, which is a switch located under the car hood overhanging the platform. From this switch the current passes to a similar one, marked b, located in a like position at the other end of the car. These two switches are called emergency switches; they are provided simply as a safety device, and are used only when the main switches get out of order and the motorman can not turn the current off in the regular way. From the last hood switch b the current passes to the bottom of the car, where it enters the wire d d at the point c. This wire d d, as will be seen, runs in both directions, and ends in the stands C C. These latter are the controlling switches, and are provided with a handle h, by means of which the current is turned on or off from the motors, and is directed through them in such a way as to make the car run in whichever direction may be desired. From the controllers C C several wires are run under the car, as shown at e e e. These wires are generally bunched into one or two cables, but they are kept separate from each other by means of strong insulating coverings. Four wires lead into each motor, and three or four into each of the boxes marked G G. If the motors were required to run in one direction only, then two wires would be sufficient to convey the current to them; but as they have to run in either direction, at least three wires are necessary, but in almost every case four are used, as the results obtained thereby are more satisfactory. The boxes G G are called rheostats, and are simply devices through which the current is run so as to reduce the speed of