Do we write books so that they shall merely be read? Don't we also write them for employment in the household? For one that is read from start to finish, thousands are leafed through, other thousands lie motionless, others are jammed against mouseholes, thrown at rats, others are stood on, sat on, drummed on, have gingerbread baked on them or are used to light pipes.

Imagine the world so greatly magnified that particles of light look like twenty-four-pound cannon balls.

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.

Probably no invention came more easily to man than heaven.

Doubt must be no more than vigilance, otherwise it can become dangerous.

Libraries can in general be too narrow or too wide for the soul.

The proof that man is the noblest of all creatures is that no other creature has ever denied it.