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Updated: May 1, 2025
It has been replaced by one of 33 inches, with which a series of admirable lunar and other photographs have been taken. Nor is the difficulty in obtaining suitable material the only obstacle to increasing the size of refractors. The "secondary spectrum," as it is called, also interposes a barrier troublesome to surmount.
He saw before him the possibility of nearly quadrupling the light-gathering capacity of the great achromatic acquired by Struve; he meditated improvements in reflectors as important as those he had already effected in refractors; and was besides eagerly occupied with investigations into the nature of light, the momentous character of which we shall by-and-by have an opportunity of estimating.
Passing now from these large reflectors to refractors, further improvements have been made in the manufacture of glass by Chance, of Birmingham, Feil and Mantois, of Paris, and Schott, of Jena; while specialists in grinding lenses, like Alvan Clark, of the U.S.A., and others, have produced many large refractors.
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