“When a boy, I was fond of reading books of elementary science. I occasionally met with statements which puzzled me—which appeared to me to be wrong; but assuming, as children do, the infallibility of the author—or perhaps I should say of a printed book—I naturally came to the conclusion that my own understanding was in fault, and became greatly disheartened. After awhile—I forget on what occasion—I applied for a solution of the puzzle to my father, who, possessing a large amount of general information, was well qualified to advise. To my great delight, he assured me that I was right and the author wrong. My unqualified faith in printed statements was now of course at an end; and a habit was gradually formed of mentally criticising almost everything I read—a habit which, however useful in early life, is, as I have found in old age, a cause of much waste of thinking power when the amount is so reduced as to render economy of essential importance. Still, through the greater part of my life, this habit of reading critically, combined as it was with the power of rapid calculation, has been of great use to me, especially in my contests with the Post Office, and, after I had joined the Department, in the revision of the thousands of Reports, Returns, and Minutes prepared by other officers.” How deep were some of the problems which in his youth he tried to fathom is shown by the following extract from his paper on Astronomy:— “Some sixty years ago, my attention having been accidentally drawn to a tide-mill for grinding corn, I began to consider what was the source of the power employed, and came to the conclusion that it was the momentum of the Earth’s revolution on its axis. The next question I asked myself was—could such power be diverted—in however slight a degree—without drawing, as it were, on the stock? Further consideration showed me that the draught required for grinding the corn was trifling in comparison with that employed in grinding the pebbles on every seashore upon the Earth’s surface; and consequently that the drain on the Earth’s momentum might suffice in the course of ages to effect an appreciable retardation in the Earth’s diurnal revolution. “I now, as usual in case of difficulty, applied to my father. He could detect no fault in my reasoning, but informed me that Laplace had demonstrated in his great work (”_La Mécanique Céleste_“) that the time occupied in the Earth’s diurnal revolution is absolutely invariable. Of course both my father and I accepted the authority as unquestionable; but I never could fully satisfy my mind on the subject, and for the greater part of my life it was a standing puzzle.”