Definition: An astrometer is a type of instrument used to measure the refractive index of an object. It consists of a prism that contains two parallel slits, and a light source that illuminates both slits simultaneously. The light from the illuminating light passes through the prism, causing it to bend back towards itself, creating an image on a screen or mirror. By measuring the angle between the image and the incident light, one can determine the refractive index of the object. This measurement is crucial
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