By plotting both curves on one sheet, one can see at a glance that the cost of repairs per locomotive falls as the efficiency of labor increases. The time in years over which the costs and efficiencies were taken is plotted on the horizontal axis. For the sake of clearness in reading the curves as well as plotting them, the vertical Fig. 65. Sunday Current Consumption Curve for an Electric Road values for the efficiency curve are indicated on the left and for the cost curve on the right. This system will again be used in the Water and Load diagram, Fig. 67. 10. Water Power and Load Curves. In Fig. 67 are shown plotted on the same sheet two curves taken from the power record of a hydro-electric plant. Curve A is called the "head" curve, the term head referring to the depth of water available to run the water turbines for the generation of power. The kilowatt curve shows the number of kilowatts generated at any time during the day or 40 1905 Fig. 66. TIME IN YEARS 1906 Locomotive Repair Curves, Showing Cost of Repairs and Efficiency of Labor 1500 9.50 WATT KILOWATT CURVE "B" 1000 9.00 1 night. The vertical values for the "head" curve are given at the right and for the kilowatt curve at the left. In finding the meaning of these curves the first point to be noticed is the rise in the kilowatt curve for a drop in the head curve. or decreases the head changes in the opposite direction. 11. Comparison Curves for Incandescent Lamps. The two curves shown in Fig. 68 represent actual tests of the efficiency of the old type carbon filament lamps and the new tungsten filament lamps and give a striking graphical picture of the improvement of the new over the old style lamp. Horizontal values represent hours burned, and vertical values candlepower of the lamps. Note that the candlepower scale has been started for convenience at 9, it being evident that if it started at 0 the curves would be higher up but otherwise the same. The meaning of the curves is clear. The carbon lamp reached the "smashing point," as it is called, in 1,000 hours, whereas the tungsten lamp had only dropped in candlepower to 91 per cent of its original value in 2,200 hours. Further, the tungsten lamp held a uniform candlepower practically for 600 hours, while the carbon lamp began to decline rapidly after 100 hours of burning. 12. Curve of Wheat Prices. The price of wheat per bushel varies considerably from year to year, as may be seen from Fig. 69. A fairly good idea of the variation can be obtained by running down the column of figures in the table, but it is not nearly as easy to carry the maximum and minimum prices as to have them pictured graphically by a curve. The curve is plotted from the data given in the table and a glance will show that the maximum price is $2 per bushel in 1888 and the minimum price 633c. in 1894. The value of such curves in all business lines where prices of commodities vary from time to time is readily seen. 13. Speed Curves for Wheels or Pulleys. The curve, Fig. 70, shows how. for a certain surface or rim speed, the revolutions |