A thunderstorm is a heat engine. Sun-warmed ground heats the air above it, that air rises because it is less dense, and as it climbs it cools and its moisture condenses into a towering cumulonimbus cloud — the tall, anvil-topped kind that brings thunderstorms. Condensation releases heat, which drives the column higher still, sometimes to twelve kilometers (7.5 miles), where high winds shear the top into an anvil. Inside, ice crystals and water droplets collide and separate electrical charge until the difference discharges as lightning, heating a narrow channel of air to tens of thousands of degrees. That superheated air expands explosively, and the shockwave reaching your ear is thunder. Because light travels almost instantly and sound takes about three seconds per kilometer, counting between flash and rumble gives a usable estimate of distance. Storms of this kind are most common on hot, humid afternoons, which is why summer evenings so often end in sudden rain.

Visual AidThe cloud the Knowledge Bank builds

For most of history, locking people up was not the punishment. A medieval or early-modern jail was a holding place where the accused waited for trial or a debtor waited to pay; sentences themselves were fines, whipping, the stocks, transportation or execution. The idea that time itself could be the penalty spread only in the late eighteenth and nineteenth centuries, alongside reformers who argued that solitude and labor might produce repentance. Small-town lockups of the 1800s were often a single room with a single officer, and their security depended on the town more than on the building. Historians of punishment stress how much these institutions reflect their society’s beliefs about people: a system built to reform assumes a person can change, while one built to remove assumes they cannot. A community’s jail is therefore an unusually honest statement of what it thinks a human being is.

A foil is a character built to bring out something in another by contrast. Jewellers named the device: a thin sheet of bright metal set behind a gem to make it shine. In fiction the contrast works best when the two characters are similar in most respects and differ in one that matters, because a difference is only visible against a shared background. A stranger who wants the same thing as the protagonist but for opposite reasons is a stronger foil than a straightforward villain. Writers also use foils to externalize a decision: placing a character who has made the other choice in front of a protagonist turns an inner argument into a scene. Watch which questions each character is allowed to ask. A foil often voices the objection the reader is forming, which lets the book answer it without ever addressing the reader directly.

Economists study how markets allocate scarce goods efficiently, and philosophers ask whether every good should be allocated that way. Michael Sandel argues that putting a price on some things corrupts them: paying children to read books can replace curiosity with calculation, and a market in queue-jumping converts a rule about fairness into a question of budget. Two objections recur. The fairness objection says a sale is only truly voluntary between equals, so desperate people cannot really consent to certain bargains. The corruption objection says the transaction degrades the good itself regardless of consent. Most countries act on both, banning markets in organs, votes and people while permitting markets in almost everything else. The disagreement is about where the line falls, and a proposal to sell something no one has ever sold is exactly the case where the argument must be made rather than assumed.