Bakerian Lecture: On the Variation of the Specific Heat of Water, with Experiments by a New Method . tal heat is generally the most usefulquantity to tabulate for experimental purposes. The numerical value of the totalheat h from 0° C to f 0. in terms of a unit at 20° C. differs but little from t over therange 0° C. to 100° C. It is, therefore, convenient to write h = t + dh, (8) where dh is the small excess of h over t at any temperature, which may appropriatelybe called the variation of the total heat. The value of dh given by Ludins formula (5) is dh = 0*84 t 100 3*8656 ^ y+6*588 t 3 ,100;
Bakerian Lecture: On the Variation of the Specific Heat of Water, with Experiments by a New Method . tal heat is generally the most usefulquantity to tabulate for experimental purposes. The numerical value of the totalheat h from 0° C to f 0. in terms of a unit at 20° C. differs but little from t over therange 0° C. to 100° C. It is, therefore, convenient to write h = t + dh, (8) where dh is the small excess of h over t at any temperature, which may appropriatelybe called the variation of the total heat. The value of dh given by Ludins formula (5) is dh = 0*84 t 100 3*8656 ^ y+6*588 t 3 ,100; 100. 2*929 t \100. (9) whence the value at 100° C. is 0-84-f6-588-3*8656--2-929 = +0*633. The corresponding formula for dh deduced from my formula (6) representing theresults of the continuous-electric method is dh = 1*1605 logio^4?^ ^1*464 J-r +0*42 t V 20 100 100 ) + 0-30 100/ (10) whence the value at 100° C. is 0*903-1*464 + 0*420 + 0*300 = +0*159, differing fromLudins formula by nearly 0*5 per cent. These two formulae are represented by the curves in fig. 6. In order to save space. 200. 100 Fig. 6. 22 PEOF. H. L. CALLENDAR ON THE VARIATION OF THE SPECIFIC Lxjdins curve from 65° C. to 100° C. is represented in three pieces, the curve beingshifted downwards through 0*200 when it reaches the upper Emit of the observations on the mechanical equivalent from 5° C to 35° C, if plottedon the same scale, would agree to 0*003 throughout his range with formula (lO), thefull curve. His experiments do not, as generally stated, afford any conclusiveevidence of a minimum at 30° C. in the specific heat. Rowland himself consideredthat, owing to the increasing magnitude and uncertainty of the radiation correctionbeyond 30° C, there might be a small error in the direction of making themechanical equivalent too great at that point (30° C), and the specific heat mightkeep on decreasing to even 40° C. The discrepancy from Ludins curve in thisregion is less than 1 i
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