Identifier: locomotiveengine09hill (find matches)
Title: Locomotive engineering : a practical journal of railway motive power and rolling stock
Year: 1892 (1890s)
Authors: Hill, John A. (John Alexander), 1858-1916 Sinclair, Angus, 1841-1919
Subjects: Railroads Locomotives
Publisher: New York : A. Sinclair, J.A. Hill (etc.)
Contributing Library: Carnegie Library of Pittsburgh
Digitizing Sponsor: Lyrasis Members and Sloan Foundation

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ctive lens. The comparative purity of the glass canbe determined by observing the appear-ance of a black line on white paper whenthe lenses are laid upon it; also by takingblueprints of lenses and comparing them. The lenses are laid on sensitized blue-print paper and exposed to the sun thesame as if they were tracings. After ex-posure, the lens making the least change 613 LOCOMOTIVE ENGINEERING. in color of the blueprint paper is adjudgedas being made of the most transparentglass.The foregoing test will give an idea as sperm candle or a gas jet. The paperscreen is glued on the sliding piece whilewet; when it becomes dry it is tight likea drumhead. The aperture in E overwhich the paper screen is placed is 6 made on bibulous paper it appears trans-lucent; the spot allows more light to passthrough it, and reflects less than the un-stained part of the paper. If, therefore,the paper be illuminated more stronglyfrom behind, it appears bright on a darkground. On the contrary, it appears dark
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to the relative value of lenses, so far astheir freedom from spherical aberrationand purity of the glass are concerned;yet other qualities of lenses, such as thevalue of short or long foci, have to bedetermined, and the question of qualityof light received from the different kindsof oil is of no little importance. Thiscan be found by using an instrument calleda photometer, which is an apparatus formeasuring the relative intensity of light.Of several kinds in use, Bunsens is to bepreferred. The photometer must be used ina darkened room—no other lights beingused except those undergoing test. Fig. II shows a photometer made ofpine wood. The strip 4 is i inch thick,4 inches wide and lo feet long. /J is apaper screen on a sliding piece of wood.C is a lamp so arranged that a lens can beput in and taken out quickly. D is a Fig. l.^ Fig. inches in diameter. In the center of thepaper screen a grease spot /i inch in diam-eter is made by means of a solution ofspermaceti dissolved in naptha and

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