Among the methods that have been presented as a means to determine the age, temperature gradient, and temperature of the earth, are two solutions based on the linear flow of heat, one by Kelvin1 and the other by Ingersoll and Zobel,2 both solutions pertaining to a non-radioactive earth. As it is somewhat difficult to visualize and interpret the equations of heat flow, an evaluation of the two solutions is given herewith in tables and figures. The range of constants chosen for the solution of the equations is ample to cover those mentioned in the literature, and the equations have been transformed and solved for the different unknowns.
Certain simplifying conditions for the physical state of the earth are assumed in order to obtain the Kelvin solution. The conditions are: (a) that the earth is a hot body, cooling by conduction, and homogeneous throughout; (b) that, initially, it . . .