A companion to the United States pharmacopia; . h every motion of the eye, and with eachwink or breath. The prism, which is expensive, may be replaced by a bit of looking-glass placed at an angle of forty-five degrees. We employ daylight in using this apparatus, but the mirror may beswung to one side and a lamp placed in the position usually occupiedby the mirror, and, if necessary, a bulls-eye lens may be interposed toincrease the light. When using artificial light the curtain is, of course, superfluous,and may be removed. UNITED STATES PHARMACOPOEIA. 1045 This simple apparatus enables us als
A companion to the United States pharmacopia; . h every motion of the eye, and with eachwink or breath. The prism, which is expensive, may be replaced by a bit of looking-glass placed at an angle of forty-five degrees. We employ daylight in using this apparatus, but the mirror may beswung to one side and a lamp placed in the position usually occupiedby the mirror, and, if necessary, a bulls-eye lens may be interposed toincrease the light. When using artificial light the curtain is, of course, superfluous,and may be removed. UNITED STATES PHARMACOPOEIA. 1045 This simple apparatus enables us also to measure easily both therate of enlargement and the actual size of an object. To ascertain thefirst, we place on the stage the stage-micrometer, and in the box asheet of paper, raised by books if necessary, so that its surface is justten inches below the centre of the eye-lens, minus the distanceof theeye-lens from the reflecting surface. Thus, if the distance from thecentre of the eye-lens to the part of the mirror-glass on the same hori-. Fig. 556.—Apparatus for Drawing. zontal line is one inch, the paper should be nine inches below the centreof the eye-lens. The tube should also be drawn out to ten inches inlength. We now focus so that the image is clear and sharp on the paper,and then measure with a foot-rule. We will suppose that ten divisions of the micrometer scale, inwhich each division is yj-^- of an inch, measure 6|- inches on the ten divisions are y1^ of an inch ; -^w of an inch is contained in 6-J-inches sixty-five times ; the rate of enlargement therefore is sixty-fivediameters. We now remove the scale and insert an object which wewish to measure. The image is measured in the same manner with therule, and the length thus determined is divided by sixty-five to ascer- 1046 A COMPANION TO THE
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Keywords: ., bookcentury1800, bookdecade1880, bookpublishernewyo, bookyear1884
