Alvan Clark & Sons: artists in optics

Three instrument makers -- Alvan Clark and his sons, George Bassett and Alvan Graham -- figured importantly in the great expansion of astronomical facilities which occurred during the second half of the 19th century. Almost every American observatory built during this period, and some observatories abroad, housed an equatorial refracting telescope, and often auxiliary apparatus as well, made by the Clarks. Their optical work, recognized as unexcelled anywhere in the world, was the first significant American contribution to astronomical instrument making. While American telescopes had been made before, none compared with those of European manufacture; by the end of the 19th century, partly because of the example set by Alvan Clark & Sons, several other Americans were making fine astronomical instruments.