From “Books for the Journey” (Aldous Huxley, 1925, Along the Road: Notes and Essays of a Tourist):

India paper and photography have rendered possible the inclusion in a portable library of what in my opinion is the best traveller’s book of all — a volume (any one of the thirty-two will do) of the twelfth, half-size edition of the Encyclopaedia Britannica. It takes up very little room (eight and a half inches by six and a half by one is not excessive), it contains about a thousand pages and an almost countless number of curious and improbable facts. It can be dipped into anywhere, its component chapters are complete in themselves and not too long. For the traveller, disposing as he does only of brief half-hours, it is the perfect book, the more so, since I take it that, being a born traveller, he is likely also to be one of those desultory and self-indulgent readers to whom the Encyclopaedia, when not used for some practical purpose, must specially appeal. I never pass a day away from home without taking a volume with me. It is the book of books. Turning over its pages, rummaging among the stores of fantastically varied facts which the hazards of alphabetical arrangement bring together, I wallow in my mental vice. A stray volume of the Encyclopaedia is like the mind of a learned madman — stored with correct ideas, between which, however, there is no other connection than the fact that there is a B in both; from orach, or mountain spinach, one passes directly to oracles. That one does not oneself go mad, or become, in the process of reading the Encyclopaedia, a mine of useless and unrelated knowledge is due to the fact that one forgets. The mind has a vast capacity for oblivion. Providentially; otherwise, in the chaos of futile memories, it would be impossible to remember anything useful or coherent. In practice, we work with generalizations, abstracted out of the turmoil of realities. If we remembered everything perfectly, we should never be able to generalize at all; for there would appear before our minds nothing but individual images, precise and different. Without ignorance we could not generalize. Let us thank Heaven for our powers of forgetting. With regard to the Encyclopaedia, they are enormous. The mind only remembers that of which it has some need. Five minutes after reading about mountain spinach, the ordinary man, who is neither a botanist nor a cook, has forgotten all about it. Read for amusement, the Encyclopaedia serves only to distract for the moment; it does not instruct, it deposits nothing on the surface of the mind that will remain. It is a mere time-killer and momentary tickler of the mind. I use it only for amusement on my travels; I should be ashamed to indulge so wantonly in mere curiosity at home, during seasons of serious business.