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Updated: June 16, 2025
Those little lenses in their silver mountings, all ground and set and fashioned by his own hand, showed him the blood-globules, and the "pipes" of the teeth, which Purkinje and Retzius found with their achromatic microscopes a century later. We honor his skill and sagacity as they deserve; but a little trick of Mr.
Yet at that time the fifteen-inch achromatic of Pulkowa had already left the workshop of Fraunhofer's successors at Munich. It was not indeed until 1845, when the impost which had so long hampered their efforts was removed, that the optical artists of these islands were able to compete on equal terms with their rivals on the Continent.
Clouds interposed, and we lost the first contact, but were more fortunate in the end, which was observed as follows: By Mr Wales with Dollond's 3 1/2 foot achromatic refractor, at 3h 28' 39" 1/4 \ By Mr Clerke with Bird's 2 feet |Appa- reflector, at 3 28 52 1/4 |rent And by me with an 18 inch reflector |time. made by Watkins, 3 28 53 1/4 / Latitude of the isle or place of observation, 20° 17' 39" S. Longitude per distance of the sun and moon, and moon and stars, 48 sets, 164° 41' 21" East.
The making of achromatic lenses for telescopes had been accomplished, it is true, by Dolland in the previous century, by the union of lenses of crown glass with those of flint glass, these two materials having different indices of refraction and dispersion.
It exhibits two breaks on the S.W., through one of which passes a coarse valley that ultimately runs on the E. side of the depressions just referred to. The interior is pitted with many craters, one on the W. side being shallow but of considerable size. I once counted twenty with a 4 inch Cooke achromatic, and Dr. Sheldon of Macclesfield subsequently noted many more.
Whenever we were at work with our microscopes at the Institute I always told her that her mind was the only achromatic one I ever looked into, I did n't say looked through. -But I did n't come to talk about that.
Then issuing from the tube, they ranged themselves around it, while its opening was hermetically sealed. In March 1821, the younger Herschel, in conjunction with Sir James South, undertook a series of observations on the distances and positions of three hundred and eighty double and triple stars, by means of two splendid achromatic telescopes of five and seven focal length.
In the neighbourhood of the valley, on either side, there are several bright craters. Three stand near the N.E. edge, and one of considerable size near the N.W. end on the opposite side. A winding cleft crosses the valley about midway, which, strange to say, is not shown in the maps, though it may be seen in a 4 inch achromatic.
He has heard it said that the chance arrangement of two pairs of spectacles, in the shop of a Dutch optician, gave the direction for constructing the first telescope. Possibly, in time, say a few geological ages, it might in some optician's shop have brought about a combination of flint and crown glass which, together, should have been achromatic.
THE ROYAL SOCIETY OF LONDON. If I were to attempt to do justice to the merits of this great society, I should have to devote many pages, to such subjects as the achromatic telescope of Dollond; the dividing engine of Ramsden, which first gave precision to astronomical observations, the measurement of a degree on the earth's surface by Mason and Dixon; the expeditions of Cook in connection with the transit of Venus; his circumnavigation of the earth; his proof that scurvy, the curse of long sea-voyages, may be avoided by the use of vegetable substances; the polar expeditions; the determination of the density of the earth by Maskelyne's experiments at Scheliallion, and by those of Cavendish; the discovery of the planet Uranus by Herschel; the composition of water by Cavendish and Watt; the determination of the difference of longitude between London and Paris; the invention of the voltaic pile; the surveys of the heavens by the Herschels; the development of the principle of interference by Young, and his establishment of the undulatory theory of light; the ventilation of jails and other buildings; the introduction of gas for city illumination; the ascertainment of the length of the seconds-pendulum; the measurement of the variations of gravity in different latitudes; the operations to ascertain the curvature of the earth; the polar expedition of Ross; the invention of the safety-lamp by Davy, and his decomposition of the alkalies and earths; the electro-magnetic discoveries of Oersted and Faraday; the calculating-engines of Babbage; the measures taken at the instance of Humboldt for the establishment of many magnetic observatories; the verification of contemporaneous magnetic disturbances over the earth's surface.
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