Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . HTHALMOSTATE. 1563 OPTICAL INSTRUMENTS. of about li inches diameter and from 6 to 12 inchesfocus, liaving a central perforation, behind which isarranged a lens through ?nhioh the eye, illuminatedby the rays from a lamp reflected into it by a mirror,is viewed. An instrument on the same principle, enabling aperson to examine the interior of his own eye, iscalled a
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Knight's American mechanical dictionary : a description of tools, instruments, machines, processes and engineering, history of inventions, general technological vocabulary ; and digest of mechanical appliances in science and the arts . HTHALMOSTATE. 1563 OPTICAL INSTRUMENTS. of about li inches diameter and from 6 to 12 inchesfocus, liaving a central perforation, behind which isarranged a lens through ?nhioh the eye, illuminatedby the rays from a lamp reflected into it by a mirror, is viewed. An instrument on the same principle, enabling aperson to examine the interior of his own eye, iscalled an auto-ophthalmoscope. It is shown in thelower portion of the tigui-e. Dr. Knapps instrument consists of two centrallyperforated plates, connected by a handle, and havingbetween them two disks each with a series of per-forations near its periphery in wliieh lenses are in-serted, those in the one being convex and in theother concave, so as to form a varied series of mag-nifiers by turning the disk so as to bring dillerentones into coincidence over the central opening inthe case. One side of the case has an annular con-cave mirror which reflects light into the eye whileit is being examined bj- a magnifier or the naked Kg. 3403.. Auto-ophthalmoscope, eye, through the central opening. One of the open-ings in each disk is left unfilled, so that only a singlelens, or no lens at all, may be used. Oph-thalmo-state. An instrument for holdingthe eye in a fixed position to facilitate operations.Such are the ophthalinostate of Jager, the fine many-pointed forceps of Graife, etc. They have specificnames, such as fixtdion-forceps, iris-hook, etc. Oph-thalmosUitmn. Ophthal-mox-ystnim. (Surgical.) A smallbrush with barbs like an ear of barley, to scarify theeyelids in cases of ophthalmia. Opsi-ome-ter. An instrument for measuringthe limits of distinct vision in difierent indiWduals, for determining the focal length of lenses suited forremedying imperfect vision. Lehots device consists of a whit