This is a companion to our previous paper in which we give a published example, based primarily on Perry's work, of a graph of ln "y" versus "t" when "y" is an exponential function of "t". This work led us to the idea that Lord Kelvin's (William Thomson's) estimate of the Earth's age was wrong not because he did not account for radioactivity, as is commonly believed, but because he used the wrong model for Earth's heat loss. We feel this idea is worth spreading. To this end (following England et al.), we examine two questions, the first about the radioactivity part and the second about Perry's alternate model for Earth's heat loss.