It is a sad hardship and slavery to people who live in towns, that in their movements they know of one dimension only; they walk along the line as if they were led on a string. The transition from the line to the plane into the two dimensions, when you wander across a field or through a wood, is a splendid liberation to the slaves, like the French Revolution. But in the air you are taken into the full freedom of the three dimensions; after long ages of exile and dreams the homesick heart throws itself into the arms of space.