In 1696, under King William III, England needed money and faced a public that regarded an income tax as an intolerable invasion of privacy. The answer was a proxy for wealth that an assessor could count from the street: windows. Every house paid a flat two shillings, with four more for 10 to 20 windows and eight more beyond 20. Adam Smith judged the tax relatively inoffensive in The Wealth of Nations because no official had to step inside. The rates kept shifting, with a 20 shilling tier for 30 or more windows in 1709 and a charge on each individual window by 1747.

The proxy failed as cities grew. Large old houses were carved into crowded tenements, landlords were billed for every pane, and many responded by boarding up the windows and leaving families in darkness during an age of cholera and tuberculosis. This episode traces how a privacy-minded compromise became known as a tax on light and air, the odd exemptions it produced, and the myths attached to it. Not every bricked-up window was a tax dodge, and scholars find no evidence that the phrase daylight robbery comes from the window tax at all.

• Dairies, cheese rooms, and milk houses were exempt, but only if the name of the room was carved into the building itself for the assessor to see.
• In 1841 the Manchester Royal Infirmary was taxed one shilling and nine pence per window for rooms occupied by its medical staff, a bill of one pound, nine shillings, and nine pence.
• Georgian architects obsessed with symmetry built blind windows on purpose when a real one would have opened onto a chimney breast or staircase.
• Scotland imposed its own version in 1748, France adopted a window tax in 1798, and Ireland followed in 1799.
• After a fierce public health campaign in the winter of 1850 and 1851, the UK repealed the tax in July 1851 and replaced it with a tax on inhabited houses. France kept its version until 1926.