[The period illustrated by the following letters includes the years between my father's return from the voyage of the Beagle and his settling at Down. It is marked by the gradual appearance of that weakness of health which ultimately forced him to leave London and take up his abode for the rest of his life in a quiet country house. In June 1841 he writes to Lyell: “My father scarcely seems to expect that I shall become strong for some years; it has been a bitter mortification for me to digest the conclusion that the ‘race is for the strong,’ and that I shall probably do little more, but be content to admire the strides others make in science.”

There is no evidence of any intention of entering a profession after his return from the voyage, and early in 1840 he wrote to Fitz-Roy: “I have nothing to wish for, excepting stronger health to go on with the subjects to which I have joyfully determined to devote my life.”

These two conditions—permanent ill-health and a passionate love of scientific work for its own sake—determined thus early in his career, the character of his whole future life. They impelled him to lead a retired life of constant labour, carried on to the utmost limits of his physical power, a life which signally falsified his melancholy prophecy.