Domain-Specific Vocabulary

What Sleep Is For

Sleep is not switching off. Parts of the brain are busier asleep than awake. Two claims are well supported. The first is that sleep consolidates memory: during deep sleep, the day's experiences are replayed and moved from short-term storage into long-term. Interrupt deep sleep and recall of the previous day drops measurably. The second is that sleep clears waste. The spaces between brain cells widen during sleep, and fluid washes through, removing proteins that build up while awake. A third claim — that a particular number of hours suits everybody — is not supported. Need varies with age and between individuals, and self-reported sleep is unreliable. Teenagers are a special case. Their body clocks genuinely shift later at puberty, which is a biological fact rather than a preference, and school start times mostly ignore it.

Canals and Railways

Between 1760 and 1830 Britain built about four thousand miles of canal. Within forty years of that, most of it was losing money. A canal boat carried thirty tons behind one horse, where a cart carried two. That was transformative for coal and stone, which are heavy, cheap and not in a hurry. But a canal cannot climb without locks, cannot be built where there is no water, and freezes. A boat averaged three miles an hour. The railways did not beat canals on cost per ton at first. They beat them on speed, on reliability, and on where they could go — a railway can cross a watershed a canal cannot. Many canal companies were bought by railway companies, sometimes specifically in order to close them. By 1900 most of the network carried nothing. Some of it is now used more than it ever was, by people on holiday.