Identifier: ironsteelmagazin10sauv (find matches)
Title: The Iron and steel magazine
Year: 1898 (1890s)
Authors: Sauveur, Albert, 1863-1939
Subjects: Metallography Iron Steel
Publisher: Cambridge, Mass. (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
itted light;that is, by light sent from below the stage through the object.Reflected light, that is, light thrown from above upon thespecimen, must of necessity be used. This light may be reflectedobliquely upon the specimen, directly from the source of light orwith the assistance of a mirror or of a condenser, or it may be AIciaIIoi:^rapliy Applied to Foundry Practice 311 reflected vertically upon the sample by the lenses themselves ofthe objective by means of a device known as a vertical illumi-nator and which affords by far the best illumination of opaqueobjects. This illuminator, which is shown in Fig. 3, consistsof a small glass disk, supported by a milled head, which controlsits position, and is inserted between the objective and the nose-of the microscope, as shown in Fig. i. The light from thesource of light enters the illuminator through a lateral apertureand is reflected downwards by the little glass disk through thelenses of the objective, which condenses the light upon the
Text Appearing After Image:
Figs. 4 and 5 sample. The light emitted by the lighted portion of the speci-men re-enters the objective, passes in part through the glassdisk, then through the eye-piece, reaching the eye of the observerand producing an enlarged image in the usual way. Obliquely vs. Vertically Reflected Light. — It will readily beseen that obliquely reflected light can be used only with rela-tively low power objectives, because high-power lenses must bebrought too close to the object to allow any beam of light toreach the latter from without. Obliquely reflected light, more-over, yields, so to speak, a negative image of the true appearanceof the sample, because the bright constituents reflecting the 312 The Iron and Steel Magazine light outside the microscope will appear dark, while the darkconstituents, by absorbing and diffusing the light, reflect someof it into the tube of the microscope and appear bright. Ver-tical illumination, on the contrary, yields a true image of theappearance of the object

Note About Images