Micrographia : containing practical essays on reflecting, solar, oxy-hydrogen gas microscopes; micrometers; eye-pieces, &c. &c. / by C.R. Goring and Andrew Pritchard.

  • C. Rosario Goring
Date:
1837
Catalogue details

Licence: Public Domain Mark

Credit: Micrographia : containing practical essays on reflecting, solar, oxy-hydrogen gas microscopes; micrometers; eye-pieces, &c. &c. / by C.R. Goring and Andrew Pritchard. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    of the aperture of the object-glass is cut off by it. On trying any telescope thus mounted, it will soon be seen whether the eye-piece is achromatic or not: or the said eye-piece may be tried as a compound microscope, by itself; and I can only say, that a man who is not able to perceive colour in it must be either utterly blinded by preconceived opinions, or by a com- plete incapacity to perceive the faults of optical instruments*. Nevertheless, there is a construction for an erecting eye- piece which is bona fide achromatic to any angle of aperture, as it appears to me, namely, a simple reduplication of the Huyghenian eye-piece ; that is, using one to erect and form the secondary image, and another to view it, which will give a com- pensation to each part; but this construction is never employed, at least I never met with it, because, I presume, if we use a Huyghenian eye-piece to form a secondary image, the com- ponent lenses will be nearly of the worst figure, and in the worst position for giving distinctness-]-,—which is a quality to be preferred even to achromatism. I need not observe that such a construction could never be used by itself, as an engiscope, or compound microscope, because its focus being negative, or between the glasses, it can only be made to operate on an image already formed. In the year 1815, being then a student in the University of Edinburgh, I began my career as a reformer of microscopes, from reading the article Telescope, in the Encyclopaedia Bri- tannica, written by Professor Robinson, and chiefly from the consideration of a passage in it, which I shall here quote. <fWe have examined trigonometrically the progress of a * Vide Chap. XIX. p. 191, and particularly p. 200, of the Microscopic Cabinet. Every thing I have there said concerning the art of looking into the defects of microscopes and engiscopes applies to erecting eye- pieces, and also to telescopes, with vei'y little modificaton. He that hath eyes to see, let him see for himself, and be made a dupe no longer, either by fine-spun theories or great authorities. t The ordinary construction rather resembles an Huyghenian eye-piece reversed, or inverted, which, of course, utterly subverts the achromatism.
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