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"At the earliest period of the employment of the camera obscura, a double-convex lens was used to produce the image; but this form was soon abandoned, on account of the spherical aberration so caused. Lenses for the photographic camera are now always ground of a concavo-convex form, or meniscus, which corresponds more nearly to the accompanying diagram."
How the human body survives a storm like this must be explained by the fact that it is exposed to it but a few moments at a time, whereas these grand old trees had had no one to take their places, from the rising to the going down of the sun. Angular bits of iron, concavo-convex, sticking in the sides of muddy depressions, showed where shells had exploded in their furrows.
The reader may readily comprehend the phenomena of refraction, by means of light passing through lenses of different curves, by reference to the following diagrams: By these it is seen that a double-convex lens tends to condense the rays of light to a focus, a double-concave to scatter them, and a concavo-convex combines both powers.
Already the solemn day of the Most Holy Lady of Flowers191 was approaching; the weather was lovely, the hour early; the clear sky was extended about the earth like a calm, hanging, concavo-convex sea.
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