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8CIOPTICON MANUAL. 29 ANALYSIS OF THE SCIOPTICOW. The lenses, mountings, &c., Fig. 15, are shown in sec- tion. What is left of the frame and cylinder, the lamp, chimney, reflector, &c., are shown in perspective. The parts are as follows: a J—Front combination of the objective cemented together. c d —Back combination separated by a ring. If the cells holding these combinations are unscrewed and the lenses removed, they must be returned in the same order and position as seen in the dia- gram. There is no need of removing them. Even the outer sur- faces of a and d will seldom need dusting if kept in a clean place with the caps closed. They should not be fingered, and the brush or fabric used for dusting them should be clean and soft. e —Milled head for adjusting the focus. //—Flange attached to the projecting wooden ring^^r. The tube here represented is a quarter-size portrait camera tube of 4\ inches back focus, requiring an aperture in g h of 2| inches in diameter. If a larger tube is used, the aperture in g h has to be enlarged. If the back focus is more than 5 inches, the extension front h k must be drawn out more or less from the main body, as is shown in the diagram. If the focus is shorter than 3J inches, the ring g g is removed, letting the flange/ back to A. h h h' —"Wooden frame of the extension front; h f sliding in a groove within the body-frame I I. i —Top of the hood covering light dispersed by reflection. The near side is cut away to show the screen k; the edge of the remain- ing side is seen beyond k. k —Is now modified into a horizontal lid, which shuts up over the lens d, darkening the picture on the screen like a falling curtain. I I —Portion of the wooden frame, the rest being mostly cut away to show the lamp, and how the extension front slides in its groove. m — Claw attached to the front foot. n —Flange under the back foot. On the top of the Sciopticon case, or box in which it is carried, and which can be placed upon a stand or table to elevate the instrument to proper height while in use, are two round-headed screws, slightly raised, and at the dis- tance apart of m n ; m clings to one, and n slips under the other,