The main specific heat
The main specific heat of a heterogeneous mass, or of a mass of homogeneous substance, under different pressures in different parts, is the quantity of heat which the whole body takes or gives in rising or in falling 1° in temperature, divided by the number of units in its mass.
The mean specific heat was adopted onto Sun by Lord Kelvin in his arguments concerning the popular discourse of his day on Sun's age.
- W. Thomson (Lord Kelvin) (March 5, 1862). On the Age of the Sun’s Heat. Macmillan's Magazine. Retrieved on July 18, 2015. “The expression, “mean specific heat” of the sun, in the text, signifies the total amount of heat actually radiated away from the sun, divided by his mass, during any time in which the average temperature of his mass sinks by 1°, whatever physical or chemical changes any part of his substance may experience.”