Some characteristics of the Marvin pyrheliometer . 4343E< (14)(15)(16) (17) If the observations, accordingly, satisfy Newtons law of cooling the plot of logJ AD\ — ) versus t will be a straight line. The slope of this straight line determines E, the coefficient of cooling. Asan illustration of this method the following examples may be cited: TABLE 1.—Cooling and Heating Curve Data, Electrical Calibration Heating Time (Rt-Ro)observed Seconds( ° 10 .00690 20 .01241 | 30 .01780 40 .02296 50 .02805 1 60 .03292 Cooling. Time Seconds 102030405060 (Rt-Ro)observed Ohms
Some characteristics of the Marvin pyrheliometer . 4343E< (14)(15)(16) (17) If the observations, accordingly, satisfy Newtons law of cooling the plot of logJ AD\ — ) versus t will be a straight line. The slope of this straight line determines E, the coefficient of cooling. Asan illustration of this method the following examples may be cited: TABLE 1.—Cooling and Heating Curve Data, Electrical Calibration Heating Time (Rt-Ro)observed Seconds( ° 10 .00690 20 .01241 | 30 .01780 40 .02296 50 .02805 1 60 .03292 Cooling. Time Seconds 102030405060 (Rt-Ro)observed Ohms 616 Bulletin of the Bureau of Standards [ TABLE 2.—Analysis of Heating and Cooling Curves, Electrical Calibration Mean time —(AR/At)i«.* *6£) —AR/At,computed Heating Cooling Mean Observed Curve Seconds5 15 531 557 544 .736 .737 546 25 539 534 536 .729 .726 532 35 516 517 516 .713 .714 518 45 509 509 509 .707 .703 505 55 487 495 491 .691 .691 491 6£*. O o *° rime in teconefj Fig. 4.—Method of plotting heating and cooling curves The plot of log ( Wersus / is given by circles in Fig. 4. Columns 6 and 7 of the above table are obtained from the valuesgiven by this plot. On account of the lag (in this case a lead) the FooU) The Marvin Pyrheliometer 617 observed value of AR/At in the interval o to 10 seconds is far toogreat. After the first 10 seconds, however, the observations lievery satisfactorily on the straight line of Fig. 4. The coefficientE determined by the slope of the straight line is E = Fromcolumns 2 and 3 it is seen that the heating curve is similar in typeto the cooling curve as demanded by the theory developed inSection IV. This series was picked at random from a large num-ber. Some of the series obtained showed exact agreement of theheating and cooling curves; others showed somewhat pooreragreement than the example cited. Since every point on thecooling curve exce
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