{"product_id":"fascinating-historical-physics-instrument-s-gravesande-s-ball-and-ring-with-oil-lamp-ca-1875-1900","title":"Fascinating Historical Physics Instrument – ’s Gravesande’s Ball and Ring with Oil Lamp (ca. 1875–1900)","description":"\u003cp\u003ePhysics demonstration instrument featuring a small oil lamp: the Ball and Ring of 's Gravesande, named after the Dutch physicist Willem Jacob 's Gravesande.\u003c\/p\u003e\n\u003cp\u003eThe 's Gravesande Ring is a classic apparatus for demonstrating thermal expansion of metals. It consists of a metal ball that fits through a metal ring at room temperature. When heated, the ball expands and no longer passes through the ring, illustrating the effect of heat on matter.\u003c\/p\u003e\n\u003cp\u003eThe base is cast iron, with a small oil lamp on top. This is likely the original lamp, as it fits precisely around the ring holder. I tested it: after heating for a while, the ball no longer fits through the ring, though it takes some time and the ball picks up soot in the process.\u003c\/p\u003e\n\u003cp\u003eThe ring can be unscrewed and moved up and down the central rod to position it around the ball.\u003c\/p\u003e\n\u003cp\u003eThe wick holder is marked with the letter R, \"Brevete\", and \"Paris\", suggesting French manufacture.\u003c\/p\u003e\n\u003cp\u003eExact age unknown, likely 1875–1900.\u003c\/p\u003e\n\u003cp\u003eTotal height: 28 cm\u003cbr\u003eBall diameter: 30 mm\u003c\/p\u003e","brand":"Rare Oil Lamps","offers":[{"title":"Default Title","offer_id":52777596649808,"sku":null,"price":230.0,"currency_code":"EUR","in_stock":false}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0918\/6620\/2448\/files\/IMG20260306102506.jpg?v=1772813540","url":"https:\/\/rareoillamps.com\/products\/fascinating-historical-physics-instrument-s-gravesande-s-ball-and-ring-with-oil-lamp-ca-1875-1900","provider":"Rare Oil Lamps","version":"1.0","type":"link"}