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The first actual inventor and constructor of an achromatic telescope was Chester Moor Hall, who was not in trade, and did not patent it. Towards the close of the eighteenth century a Swiss named Guinand at last succeeded in producing larger flint-glass discs free from striae.
Under suitable conditions, it can be seen as such in a 4 inch achromatic. It is easily traceable as a rill in a photograph of the N. polar region of the moon taken by MM. Henry at the Paris Observatory, and recently published in Knowledge. LE MONNIER. A great inflection or bay on the W. border of the Mare Serenitatis S. of Posidonius.
In taking photographs from these mirrors, a movement of the sensitive plate of only one-hundredth of an inch will render the image perceptibly less sharp. It was this accuracy of convergence of the light which led Dr. Draper to prefer the mirror to the achromatic lens. He has taken almost all the daily phases of the moon, from the sixth to the twenty-seventh day, using mostly some of Mr.
The king of Bavaria followed his example by ordering a still finer instrument for the same purpose; and the king of France, with a liberality still more patriotic, has had executed in his own capital, an achromatic telescope, surpassing them all in magnitude and power.
Paul of old; and what is more, dazzle and weary our eyes, like clumsy microscopists, by looking too long and earnestly through the imperfect and by no means achromatic lens. Enough. I will think of something else. I will think of nothing at all Stay. There was a sound at last; a light footfall.
A distinct crater-row runs round its outer border on the W., and ultimately, as a delicate cleft, strikes across the Mare to the E. side of Ritter. Both crater-row and cleft are easy objects in a 4 inch achromatic under morning illumination.
Dollond subsequently proved that by combining two different kinds of glass, the colours can be extinguished, still leaving a residue of refraction, and he employed this residue in the construction of achromatic lenses lenses yielding no colour which Newton thought an impossibility.
Cavendish d includes a coarse cleft on its floor, running from N. to S., which I have frequently glimpsed with a 4 inch achromatic. There are two other delicate clefts running from the Gassendi region to the S.W. side of Mersenius, which are in part crater-rills.
A microscope magnifying 400 diameters was a chef d'oeuvre of the opticians of that day; and, at the same time, by no means trustworthy. But a magnifying power of 400 diameters, even when definition reaches the exquisite perfection of our modern achromatic lenses, hardly suffices for the mere discernment of the smallest forms of life.
One is painted with the most brilliant hues of Romanticism, and glows with the essence of the Romantic spirit Aspiration; the other looks at life through an achromatic lens, and is a catalogue of Realities. To a certain extent, the difference is the difference between the bubbling energy of youth and the steady energy of middle age.
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