Electricity for public schools and colleges . ns of Professor Tait, Sir W. Thomson, and others,it is found that the thermo-relations of most metals for all temper-atures (at least for a wide range of temperature) can be simplyexhibited in one diagram. We shall give and explain this graphicmethod ; the reader understanding that the construction of thediagram follows from ythe experimental resultsgiven in §§ 5 and fig. i. O 7 is the axisof ordinates, alongwhich measurementsrepresent micro-volts ;and O /° is the axis ofabscissre along whichmeasurements repre-sent degrees diagr
Electricity for public schools and colleges . ns of Professor Tait, Sir W. Thomson, and others,it is found that the thermo-relations of most metals for all temper-atures (at least for a wide range of temperature) can be simplyexhibited in one diagram. We shall give and explain this graphicmethod ; the reader understanding that the construction of thediagram follows from ythe experimental resultsgiven in §§ 5 and fig. i. O 7 is the axisof ordinates, alongwhich measurementsrepresent micro-volts ;and O /° is the axis ofabscissre along whichmeasurements repre-sent degrees diagram is drawnto scale suitably, sothat the lengths of or-dinates and abscissaegive viicro-volts and de-grees respectively; butthe ordinates and ab-scissae need not bemeasured in the sameunits of length respec-tively. The three straight lines given represent the metals lead,metal A, and metal B, respectively ; in what sense they rtint-sent these metals will soon be seen. Let us erect ordinates from the points /._,, I, and /,, on the line s 2. 260 ELECTRICITY en. xvi. O /, answering to the temperatures f.,°, t°, and t° C, respectively ;and let A L and B L measure the thermo-electric powers of1/iefaI A, and metal B, respectively, with respect to lead at t^ C,so that also A B represents the thermo-electric power of A withrespect to B at /° C. Let /, and /^ be equidistant from /, so — i = t — t^. Then by simple geometry the area of the trapezium Aj A.^ L2 Ljis given by the product A L x L, Lo ; that is, by the productof the thermo-electric power at t° C, measured by A L, intothe difference of temperature t^ - ty of the junctions, measured by LjL, ; where t = -. But by the result of experiment as given in § 5, this product gives us the E of a cell composed of the meial A and kad^ in which the junctions are at t^ and /,. Hence we have that if the line A L measure the thermo-electricpower of vietal A with respect to lead at t° C, then the area Ai A., Lo Li g
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