Transactions . it the arc at any height upon the rod. This rod is ofhighly polished steel, nickel-plated, 9 mm. in diameter and 48 length ; it is screwed firmly at its lower end into the heavy brassclamp, E, which may be fastened to the edge of a table, mantel-shelf,bracket, or other convenient support, by means of a heavy thumb-screw, with a revolving washer at the top, allowing a firm graspwithout tearing or fraying the underside of whatever woodwork itmay be attached to. 585 Upon the front of the clamp E, by a half bayonet fastening, sothat it may be unshipped and laid aside when not
Transactions . it the arc at any height upon the rod. This rod is ofhighly polished steel, nickel-plated, 9 mm. in diameter and 48 length ; it is screwed firmly at its lower end into the heavy brassclamp, E, which may be fastened to the edge of a table, mantel-shelf,bracket, or other convenient support, by means of a heavy thumb-screw, with a revolving washer at the top, allowing a firm graspwithout tearing or fraying the underside of whatever woodwork itmay be attached to. 585 Upon the front of the clamp E, by a half bayonet fastening, sothat it may be unshipped and laid aside when not in use, is attachedthe arm, D, carrying at its other end the crutch-piece, C, intended tosupport the chin of the patient. The arm proper is about 30 , of square tubing, and receives into its open end another slid-ing piece, allowing the whole to be lengthened to cm., men-tioned as the radius of the arc B, and the proper distance for theeye to be from the point of fixation, C. Another piece of square. tubing is fastened at right angles and perpendicularly to this piece,in which slides the square nickel-plated rod, C, carrying upon itsupper end a curved piece of smooth nickel-plated brass, upon whichthe chin rests. This rod may be fastened at any height upon thearm, D, by a small thumb-screw, F, so that the height of the crutchand the arc B may be made to correspond respectively to the heightsof the chin and the eye of the patient. Fig. 2 shows the reverse side of the arc B, the prolongation of theaxis backward, the rod. A, upon which it slides, and the thumb-screw fastening. On the left-hand side of the axis as the patient 586 sits facing it, directly on the horizontal line, is an index, c, pointingto radiating lines on the reverse surface of the arc. These radii aredrawn around the axis in spaces of 30°, numbered as the opticiansnow reckon, the axes of cylindrical lenses (as the Society has this yeargiven its approval) at zero for the left horizontal line, a
Size: 1669px × 1497px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, booksubjectophthalmology, bookye
