Lens
2 of the 6 encyclopedias on this shelf carry an entry for Lens. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a transparent body, usually of glass, bounded by two curved surfaces, or by a curved surface and a plane. The name is derived from the lentil, which is shaped like a double convex lens. Lenses are of two sorts. Those that bring rays of light to an actual focus are called converging or convex lenses. They form a real image. Lenses that cause rays of light to diverge, as though they proceeded from a point, are called diverging or concave lenses. The former are bounded by convex surfaces and give a magnified image. They are known also as magnifying glasses. The origin of lenses is not clear. The British Museum has a ground rock crystal found by Layard in excavations at Nimrud. A simple magnifying glass is described by an Arabic writer of 1052. The invention of spectacles is credited to an Italian of about 1255. The combination of lenses to form a compound microscope is credited to an optician named Janssen of Holland, dating about 1590. Galileo invented the telescope in 1610. The largest lenses known are those made for modern telescopes. A large lens was made for the Carnegie Solar Observatory on Mount Wilson, California. The block of glass was cast in a village near Paris. It was transported to Pasadena. An optician spent three years in grinding and polishing it. When complete, it measured sixty inches across, it was eight inches thick at the middle point , and weighed an even 20,000 pounds. The surface was so delicate, so polished, that the touch of a visitor's finger would have meant ruin. The finished lens was packed securely in soft material and was carted up the mountain side by a road constructed for the purpose. See Lentil ; Spectacles ; Thallium ; Telescope ; Clark
Collier's New Encyclopedia (1921)
a town of France, in the TORY. de - Calais department, 9 miles N. W. Arras. Has coal mines and sugar
What Has Changed in the Last Century
Aiton's 1910 account credits Galileo with inventing the telescope in 1610; the modern view gives priority to Hans Lippershey, who applied for a patent in the Netherlands in 1608, with Galileo building his own instrument the following year. Its "largest lenses known" claim has also aged: the 60-inch Mount Wilson instrument it describes was in fact a reflecting telescope, whose big glass disc was a mirror, and the largest telescope lens ever put to work remains the 40-inch refractor at Yerkes, finished in 1897 — glass that size sags under its own weight, so no one has surpassed it. Since 1910 the lens itself has been remade in materials the entry never imagined: moulded plastics, aspheric and gradient-index designs, anti-reflection coatings, soft contact lenses from 1971, and the multi-element stacks a few millimetres wide inside every smartphone. The other Lens, the French coal town Collier's noted for "coal mines and sugar" in 1921, had just been levelled in the First World War; its last pits closed by 1990, the mining basin became a UNESCO World Heritage site in 2012, and a branch of the Louvre opened there the same year.
Written for this edition, 2026.