phototachometern.
/ˌfəʊtəʊtaˈkɒmᵻtə/, /ˌfəʊtəʊtəˈkɒmᵻtə/, U.S. /ˌfoʊdoʊˌtæˈkɑmədər/, /ˌfoʊdoʊtəˈkɑmədər/ 1. Physics. An apparatus for measuring the speed of light. Now rare.
ΘΚΠ
the world > matter > physics > electromagnetic radiation > light > emission of light, radiation > [noun] > speed of light > instrument for measuring
phototachometer1884
1884 Science 16 May 588/2 A re-determination of the velocity of light by the phototachometer.
1886 Athenæum 3 July 21/1 An account of Prof. Newcomb's determination..of the velocity of light. The apparatus employed, to which the name of ‘phototachometer’ was given.
1902 Science 18 July 82/1 The very accurate results..of Newcomb with his highly refined phototachometer in this country.
2. An optical device for measuring the speed of rotation of a part.
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1973 Electrochimica Acta 18 294/2 Accurate and rapid measurement of rotation rate was achieved with a digital counter activated by a photo-tachometer.
1983 Science 16 Dec. 1182 (advt.) [A centrifuge] Unique see-through lid—you see the rotor in operation and can easily..verify speed with a phototachometer.
2001 Business Wire (Nexis) 29 Nov. A phototachometer to measure the rotational rate of the vehicle's driveshaft.
This entry has been updated (OED Third Edition, March 2006; most recently modified version published online March 2022).
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n.1884