This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1830 Excerpt: ...be twice that of the former. Hence we must conclude, that the nearer we can bring an object to the eye the larger it will appear. Now, if we have to examine a very minute object, and in order to render its parts distinguishable if we bring it very near to the eye, (suppose one or two inches, ) it will become very ...
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1830 Excerpt: ...be twice that of the former. Hence we must conclude, that the nearer we can bring an object to the eye the larger it will appear. Now, if we have to examine a very minute object, and in order to render its parts distinguishable if we bring it very near to the eye, (suppose one or two inches, ) it will become very indistinct and confused. This effect is produced by the great divergency of the rays of light from the object, and the power of the crystalline lens of the eye not being sufficient to collect the rays, whereby an image of the object may be formed on the retina, at the proper distance on the back of the eye. Now if we employ a single micrr- scope, which consists of a convex lens usually made of glass, (though it would have the power of magnifying or increasing the angle, if made of any other transparent substance, but in a different degree, ) and mounted in a brass settinr, and place it between the object and the eye, the former being in the focus of the glass, the diverging rays from the object will be refracted and rendered parallel by the lens: and thus we shall obtain a distinct and near view of the object. To exemplify this fact more simply, let A(/ig. 32) be a small object which we desire to examine. Now, bundles of rays will diverge from every part of this object in all directions, as shown by the lines A r, A r. And it there be waced before this object a convex lens B, whose focal distance is B A, those rays diverging from the object which fall on tiie surface of the lens will be refracted at its two surfaces, and emerge from it nearly parallel to each other; consequently the object is capable of being received by the eye on the side B, under a greater angle than it could be seen without the lens. '(51.) Having shown that the magnitude is...
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