Microscopic illustrations of living objects, their natural history, &c. &c / by Andrew Pritchard ; with researches concerning the most eligible methods of constructing microscopes and instructions for using them by C.R. Goring.
- Pritchard, Andrew, 1804-1882.
- Date:
- 1838
Licence: Public Domain Mark
Credit: Microscopic illustrations of living objects, their natural history, &c. &c / by Andrew Pritchard ; with researches concerning the most eligible methods of constructing microscopes and instructions for using them by C.R. Goring. Source: Wellcome Collection.
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![U] AO MICROSCOPIC ILLUSTRATIONS. not enough, when collected at 1, sufficiently to stimulate the eye, any minute pore, striaz, or other marking at A, will not be rendered visible; whilst, from the increase of aperture in the achromatic lens, 6, 6, allowing much more light from a, to fall upon it, and to be transmitted through it and collected at 7, every marking, &c. at a, will be clearly represented at 7; andthe eye, being powerfully acted upon by this increase of light, will become highly sensible of it. The angles 8, A, B, and 4, a, 6, are the angles of aperture of the respective object-glasses; and the quantity of light collected and transmitted by each will be as the squares of B, B, and @, 4, the focal lengths being equal. Hence it is that the power of a microscope, or that faculty it possesses to render the structure of an object visible, depends upon the angle of aperture of its object- glass, and not upon its magnifying power alone. But it may be supposed, perhaps, from this reasoning, that if we throw a greater quantity of light upon an object, so that more may be collected by the object-glass, we shall be the better able to define its structure ; which would probably be the case if the additional light could be thrown only upon those minute parts which we wish to examine, and not upon the whole object. But as we cannot do this—as the increase of illumination cannot be made to increase the relative proportions of light which proceed from these minute parts, the intended advantage will not be derived. Having shewn, however, that the goodness of a](https://iiif.wellcomecollection.org/image/b33289360_0046.jp2/full/800%2C/0/default.jpg)
