A good metaphor is something even the police should keep an eye on.

It thunders, howls, roars, hisses, whistles, blusters, hums, growls, rumbles, squeaks, groans, sings, crackles, cracks, rattles, flickers, clicks, snarls, tumbles, whimpers, whines, rustles, murmurs, crashes, clucks, to gurgle, tinkles, blows, snores, claps, to lisp, to cough, it boils, to scream, to weep, to sob, to croak, to stutter, to lisp, to coo, to breathe, to clash, to bleat, to neigh, to grumble, to scrape, to bubble. These words, and others like them, which express sounds are more than mere symbols: they are a kind of hieroglyphics for the ear.

Honest unaffected distrust of human abilities under all circumstances is the surest sign of strength of mind.

It is a sure evidence of a good book if it pleases us more and more as we grow older.

Just as we outgrow a pair of trousers, we outgrow acquaintances, libraries, principles, etc., at times before they're worn out and times - and this is the worst of all - before we have new ones.

The great trick of regarding small departures from the truth as the truth itself - on which is founded the entire integral calculus - is also the basis of our witty speculations, where the whole thing would often collapse if we considered the departures with philosophical rigour.

The more experiences and experiments accumulate in the exploration of nature, the more precarious the theories become. But it is not always good to discard them immediately on this account. For every hypothesis which once was sound was useful for thinking of previous phenomena in the proper interrelations and for keeping them in context. We ought to set down contradictory experiences separately, until enough have accumulated to make building a new structure worthwhile.