Leslie’s canisters

A recent BBC Radio 4 series addressed ‘Laws that aren’t Laws’, amusing rules of thumb that, like the Ig Nobel prizes, make you laugh and then think. Stigler’s Law, for example, states that every named law was actually dreamed up by someone else. Veteran readers of this column may have spotted a similar pattern for apparatus. Abderhalden’s drying pistol was invented by Ludwig Storch, Liebig’s condenser goes back to Christian von Weigel and Johan Gadolin, while the Perkin triangle was first made by the forgotten Leonard Thorne. But as with all ‘laws’, exceptions are always interesting, John Leslie really did invent the Leslie canister or cube. He also established a rule that bears another name: Ohm’s Law.