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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    fatigued with the deepest single magnifiers : whatever instru- ment shews an object best will fatigue the sight least, be it what it may, as must be self-evident. I see you have rolled yourself up like a hedgehog, and present nothing to me but a ball of prickles, let me turn you over which way I like: however, if you are not afraid of meeting with an instrument you may chance to like better than your own, pray look at these scales of the podura in the engiscope. Afraid, indeed! a likely joke.—[He looks.] Can you say you have seen this object as well in your single, or I will say compound, magnifiers? say, on your honour! I cannot say, upon my honour, that [ have seen the lines so dark, and so decidedly made out; but the circumstance is easily accounted for by the superior darkness of the engiscope, which I need not say must be much greater than that of a single lens of the same power and angular aperture, having, of course, an opening equal in size to the visual pencil of the engiscope. Well, sir, that circumstance need not distress you; if making instruments darker will cause them to perform better, we can, God be praised, darken your single lenses for you to any required degree, with coloured glasses; but 1 will defy you to shew the object with them as you have seen it just now, do what you will with them ; not only are the lines shewn darker, and the spaces between them clearer, than ivith your lenses, but many which with single or compound magnifiers, of high powers, seem ragged and dotted, or rather an aggregation of dots, are shewn as veritable lines; moreover, you see the out- line of the scale best at the same adjustment which serves also to bring out the lines*. * My coadjutor, whose experience is very great, assures me, that this circumstance depends upon the state of correction in the objective as to sphericity,—the aberration of which must be overbalanced to exhibit the
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