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    Naturevolume 114page21 (1924) | Download Citation



    EYEPIECES USED BY SIR WILLIAM HERSCHEL.—It is well known that Sir William Herschel stated that at times he used eyepieces giving magnifying powers in the neighbourhood of 6000. The eyepieces themselves seem to have been lost sight of after his death, and considerable scepticism as to the reality of these powers was expressed by subsequent writers. But recently, Dr. W. H, Steavenson, who was making by request a thorough examination of the Herschel instruments at Slough, found the eyepieces in question, and measured their powers with a dynamometer. He found values agreeing within 10 per cent, of those stated by Herschel, the highest power being well over 6000. This was naturally a single lens, gV inch in diameter. From a highly enlarged photograph the lens was seen to be not a natural spherical drop, but carefully figured. The curves were hyperbolae rather than circles, and the two sides were not quite symmetrical, but Dr. Steavenson found that he could get fair definition on a portion of Saturn: the diameter of the well-defined region was only 26”, so that it must have been excessively difficult to keep objects in the field without equatorial mounting. It is satisfactory that Sir William Herschel's accuracy of statement is once more vindicated.

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