This Postscript puzzled me sorely. “He is far too sensible a man,” I thought, “to have become a Fatalist. And yet what else can he mean by it?” And, as I folded up the letter and put it away, I inadvertently repeated the words aloud. “Do you believe in Fate?” The fair ‘Incognita’ turned her head quickly at the sudden question. “No, I don’t!” she said with a smile. “Do you?” “I—I didn’t mean to ask the question!” I stammered, a little taken aback at having begun a conversation in so unconventional a fashion. The lady’s smile became a laugh—not a mocking laugh, but the laugh of a happy child who is perfectly at her ease. “Didn’t you?” she said. “Then it was a case of what you Doctors call ‘unconscious cerebration’?” “I am no Doctor,” I replied. “Do I look so like one? Or what makes you think it?” She pointed to the book I had been reading, which was so lying that its title, “Diseases of the Heart,” was plainly visible. “One needn’t be a _Doctor_,” I said, “to take an interest in medical books. There’s another class of readers, who are yet more deeply interested——” “You mean the _Patients_?” she interrupted, while a look of tender pity gave new sweetness to her face. “But,” with an evident wish to avoid a possibly painful topic, “one needn’t be _either_, to take an interest in books of _Science_. Which contain the greatest amount of Science, do you think, the books, or the minds?” “Rather a profound question for a lady!” I said to myself, holding, with the conceit so natural to Man, that Woman’s intellect is essentially shallow. And I considered a minute before replying. “If you mean _living_ minds, I don’t think it’s possible to decide. There is so much _written_ Science that no living person has ever _read_: and there is so much _thought-out_ Science that hasn’t yet been _written_. But, if you mean the whole human race, then I think the _minds_ have it: everything, recorded in _books_, must have once been in some _mind_, you know.” “Isn’t that rather like one of the Rules in Algebra?” my Lady enquired. (“_Algebra_ too!” I thought with increasing wonder.) “I mean, if we consider thoughts as _factors_, may we not say that the Least Common Multiple of all the _minds_ contains that of all the _books_; but not the other way?” “Certainly we may!” I replied, delighted with the illustration. “And what a grand thing it would be,” I went on dreamily, thinking aloud rather than talking, “if we could only _apply_ that Rule to books! You know, in finding the Least Common Multiple, we strike out a quantity wherever it occurs, except in the term where it is raised to its highest power. So we should have to erase every recorded thought, except in the sentence where it is expressed with the greatest intensity.” My Lady laughed merrily. “_Some_ books would be reduced to blank paper, I’m afraid!” she said. “They would. Most libraries would be terribly diminished in _bulk_. But just think what they would gain in _quality_!”