Engineering Wonders of the World
Volume I

254 ENGINEERING WONDERS OF THE WORLD. Fig. 2.—INTERIOR VIEW OF THE CAR SHOWING B, A BRACKET PRO- JECTING UPWARDS FROM THE DRAWBAR SPRING AND OPERATING P, A STYLOGRAPHIC PEN. W IS THE WORK-RECORDING MACHINE. geared to a measuring wheel, which rolls on the rail, and can be lowered or raised from within the car at will. This measuring wheel is shod with a very hard steel tyre to minimize wear, and is accurately ground to make a certain number of revolutions per mile. Pressure on the drawbar moves the pen sideways across the paper, so that the dis- tance between its line and that given by a second and fixed pen (the datum line) fluctuates proportionately to the inten- sity of the drawbar pull. The speed of the train at any move- ment is shown in front of the operator by a pointer on a dial (see Fig. 3). A permanent speed record is provided by a clock and electric pen me- chanism, which makes a mark on the travelling roll of paper every two seconds or every half-second, according to the nature of the experiment. As the roll moves at a speed pro- portionate to that of the train, the higher the velocity the further apart are the marks. By means of a special scale the exact speed can be read off. There are several of these elec- trically-controlled pens which can be used for a variety of purposes. To obtain records of work done the factors of distance travelled and drawbar effort must be multiplied together. This is performed by the very ingenious machine (W, in Fig. 2) seen to the right of the car. It consists of a horizontal cir- cular table driven by the rail wheel, and of a small wheel mounted vertically in a frame above this table, so that its edge bears against it. The frame is connected with the drawbar spring, and is free to move across the horizontal table from centre to edge in a direction parallel to the axis of the vertical wheel. Owing to this wheel being in. Fig. 3.—ANOTHER INTERIOR VIEW, SHOWING DP, THE DIAL RECORD- ING THE DRAWBAR PULL, AND S, THE SPEED-INDICATING DIAL.