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See also:CAMERA LUCIDA , an See also:optical See also:instrument invented by Dr See also:- WILLIAM
- WILLIAM (1143-1214)
- WILLIAM (1227-1256)
- WILLIAM (1J33-1584)
- WILLIAM (A.S. Wilhelm, O. Norse Vilhidlmr; O. H. Ger. Willahelm, Willahalm, M. H. Ger. Willehelm, Willehalm, Mod.Ger. Wilhelm; Du. Willem; O. Fr. Villalme, Mod. Fr. Guillaume; from " will," Goth. vilja, and " helm," Goth. hilms, Old Norse hidlmr, meaning
- WILLIAM (c. 1130-C. 1190)
- WILLIAM, 13TH
William See also:Hyde See also:Wollaston for See also:drawing in See also:perspective. Closing one See also:eye and looking vertically downwards with the other through a slip of See also:plain See also:glass, e.g. a See also:microscope See also:cover-glass, held See also:close to the eye and inclined at an See also:angle of 450 to the See also:horizon, one can see the images of See also:objects in front, formed by reflection from thesurface of the glass, and at the same See also:- TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
- TIME, MEASUREMENT OF
- TIME, STANDARD
time one can also see through the transparent glass. The virtual images of the objects appear projected on the See also:surface of a See also:sheet of See also:paper placed beneath the slip of glass, and their outline can be accurately traced with a See also:pencil. This is the simplest See also:form of the camera lucida. The See also:image (see fig. 1) is, however, inverted and Eye
perverted, and it is not very See also:bright owing to
the poor reflecting See also:power of unsilvered glass.
The brightness of the image is sometimes in-
creased by silvering the glass; and on removing
a small portion of the See also:silver the observer can See also:object see the image with See also:part of the See also:- PUPIL (Lat. pupillus, orphan, minor, dim. of pupus, boy, allied to puer, from root pm- or peu-, to beget, cf. "pupa," Lat. for " doll," the name given to the stage intervening between the larval and imaginal stages in certain insects)
pupil while he
See also:sees the paper through the unsilvered See also:aperture c ,< with the remaining part. This form of the in- Image strument is often used in See also:conjunction with the FIG. I. microscope, the See also:mirror being attached to the eye-piece and the See also:tube of the microscope being placed horizontally.
About the beginning of the 19th See also:century Dr Wollaston in-vented a See also:simple form of the camera lucida which gives bright and erect images. A four-sided See also:prism of glass is constructed having one angle of 90°, the opposite angle of 135°, and the two remaining angles each of 67z°. This is represented in See also:cross-See also:section and in position in fig. 2. When the pupil of the eye is held See also:half over the edge of the prism a,
one sees the image of the object with one half of the pupil and the paper with the other half. The image is formed by successive See also:total reflection at the surfaces
b c and a b. In the first See also:place an inverted image (first image) is formed in the See also:face b c, and then an image of this
image is formed in a b, and it is the e,
2nd Image
outline of this second image seen See also:pro-
jected on the paper that is traced by the FIG. 2.
pencil. It is desirable for two reasons that the image should See also:lie in the See also:plane of the paper, and this can be secured by placing a suitable See also:lens between the object and the prism. I£ the image does not lie in the plane of the paper, it is impossible to see it and the pencil-point clearly at the same time. Moreover, any slight See also:movement of the See also:head will cause the image to appear to move relatively to the paper, and will render it difficult to obtain an accurate drawing.
Before the application of See also:photography, the camera lucida was of considerable importance to draughtsmen. The advantages claimed for it were its cheapness, smallness and portability; that there was no appreciable distortion, and that its See also:- FIELD (a word common to many West German languages, cf. Ger. Feld, Dutch veld, possibly cognate with O.E. f olde, the earth, and ultimately with root of the Gr. irAaror, broad)
- FIELD, CYRUS WEST (1819-1892)
- FIELD, DAVID DUDLEY (18o5-1894)
- FIELD, EUGENE (1850-1895)
- FIELD, FREDERICK (18o1—1885)
- FIELD, HENRY MARTYN (1822-1907)
- FIELD, JOHN (1782—1837)
- FIELD, MARSHALL (183 1906)
- FIELD, NATHAN (1587—1633)
- FIELD, STEPHEN JOHNSON (1816-1899)
- FIELD, WILLIAM VENTRIS FIELD, BARON (1813-1907)
field was much larger than that of the camera obscura. It was used largely for copying, for reducing or for enlarging existing drawings. It will readily be understood, for example, that a copy will be half-See also:size if the distance of the object from the instrument is See also:double the distance of the instrument from the copy. (C. J.
End of Article: CAMERA LUCIDA
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