Elements of natural philosophy (Volume 2-3) . es occupy a position wherein they constitute a single lens, an image of the disk will be formed as before at m; but when one of the semi-lenses is brought into the position denoted Move one Lalf . , the lens; by the dotted lines in the figure, having its optical cen-tre at E\ in a line through m, parallel to m! E, twoimages, tangent to each other, will again be formed ;for all the rays from the centre of the disk, refractedby the semi-lens in this second position, will be paral-lel to m E\ and 0 m\ is one of these rays. It isobvious also, that the
Elements of natural philosophy (Volume 2-3) . es occupy a position wherein they constitute a single lens, an image of the disk will be formed as before at m; but when one of the semi-lenses is brought into the position denoted Move one Lalf . , the lens; by the dotted lines in the figure, having its optical cen-tre at E\ in a line through m, parallel to m! E, twoimages, tangent to each other, will again be formed ;for all the rays from the centre of the disk, refractedby the semi-lens in this second position, will be paral-lel to m E\ and 0 m\ is one of these rays. It isobvious also, that the distance E E\ through which themovable semi-lens has passed, is equal to the diameterof the disk. The dynameterconsists of two , and G D, mov-ing freely one with-in the other, the lar-ger having a metal- -lie base with anaperture in the cen-tre, over which, toqualify the light, isplaced a thin slipof mother-of-pearlP. In the oppo-site end of thesmaller tube, twosemi-lenses E E\are made to moveby each other bymeans of an ar- Fig. Essential parts ofthe dynameter; Tiff. 60.
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Keywords: ., bookcentury1800, booksubjectmechanics, booksubjectopticsandphoto
