. The microscope and its revelations. pist will find it desirable to provide himselfwith some means of measuring the thickness of his cover-glass ; andthis is especially needed if he is in the habit of employing objectiveswithout adjustment, which are corrected to a particular small screw-gauge of steel, made for measuring the thickness ofrolled plates of brass, and sold at the tool-shops, answers this purposevery well; but Rosss lever of contact (fig. 372). devised for thisexpress purpose, is in many respects preferable. This consists of asmall horizontal table of brass, mounted up
. The microscope and its revelations. pist will find it desirable to provide himselfwith some means of measuring the thickness of his cover-glass ; andthis is especially needed if he is in the habit of employing objectiveswithout adjustment, which are corrected to a particular small screw-gauge of steel, made for measuring the thickness ofrolled plates of brass, and sold at the tool-shops, answers this purposevery well; but Rosss lever of contact (fig. 372). devised for thisexpress purpose, is in many respects preferable. This consists of asmall horizontal table of brass, mounted upon a stand, and havingat one end an arc graduated into twenty divisions, each of which re-presents the 171\y()th of an inch, so that the entire arc measures ,,,th of an inch ; at the other end is a pivot on which moves a long anddelicate level- of steel, whose extremity points to the graduated ai-c,whilst it has very near its pivot a sort of projecting tooth, whichbears it against a vertical plate of steel that is screwed to the. FIG. 372.—Rosss lever of contact. horizontal table. The piece of thin glass to be measured being in-serted between the vertical plate and the projecting tooth of thelever, its thickness in thousandths of an inch is given by the numberon the graduated arc to which the extremity of the lever , if the number be 8, the thickness of the glass is 008, or the j-^thof an inch. It will be found convenient to sort the covers accordingto their thicknesses, and to keep the sortings apart, so that theremay be a suitable thickness of cover for each object. But it is wellto remember that, with the exception of objects to which from theirsi/.e or nature it is impossible to apply high powers, it is better tomount the object so that, if it be required or desirable, high powersmay be used upon it. Another simple and very efficient cover-glass tester is made bvZeiss, of .Jena, and illustrated ill fig. 373. It will bo seen that themeasurement is effected
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectmicrosc, bookyear1901
