If one focuses an auxiliary microscope, carried in the inner tube, on the image situated in the back focal plane of the objective of a distant object, and then on the dust particles lying on a slide pressed against the end of the outer tube, the displacement of the auxiliary microscope gives the distance of the back focal plane of the objective from the end of the outer tube. [Please select]
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In some cases, the eye focuses the light before it reaches the retina. [Please select]
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Wherever he focuses his survey a spot glows vividly. [Please select]
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I should have studied the eggs of the Planorbis, a glairy nebula wherein focuses of life are condensed even as suns are condensed in the nebulae of the heavens. [Please select]
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