The elements of astronomy; a textbook (1919) (14595646428)

Identifier: elementsofastro00youn (find matches)

Title: The elements of astronomy; a textbook

Year: 1919 (1910s)

Authors: Young, Charles A. (Charles Augustus), 1834-1908 Young, Anne Sewell, b. 1871., ed

Subjects: Astronomy Constellations

Publisher: Boston, New York (etc.) Ginn and Company

Contributing Library: The Library of Congress

Digitizing Sponsor: The Library of Congress

Text Appearing Before Image:

Chronograph.—At present such observations areusually made by the help of electricity. The clock is soarranged that at every other beat of the pendulum an electriccircuit is made or broken for an instant, and this causes asudden sideways jerk in the armature of an electric magnet,like that of a telegraph sounder. This armature carries apen, which writes upon a sheet of paper moving beneath it.The sheet is wrapped around a cylinder six or seven inchesin diameter, and the cylinder itself turns uniformly once aminute : at the same time the pen-carriage is drawn slowlyalong, so that -the marks on the paper form a continuousspiral, graduated off into two-second spaces by the clockbeats. When taken off the cylinder, the paper presents theappearance of an ordinary page crossed by parallel lines, 418 APPENDIX. (§547 spaced off into two-second lengths, as shown in Fig. 152, whichis a part of an actual record. n rvuuuuuuwwuuiA. —n n Fig. 152.— A Chronograph Record. 9 h. 36 m. 00.0 s. A_n

Text Appearing After Image:

Fig. 153. —A Chronograph hy Warner & Swasey. The observer at the moment of a star-transit merely pressesa key. which he holds in his hand, and thus interpolates a markof his own among the clock beats on the sheet; as, for instance, §547) THE MERIDIAN CIRCLE. 419 at X and T in the figure. Since the beginning of each minuteis indicated on the sheet in some way by the mechanism ofthe clock beats, it is very easy to read the time of X and Y byapplying a suitable scale, the beginning of the mark being thetrue moment of observation. In the figure, the initial minute,marked when the chronograph was started, happened to be 9hours, 35 minutes, the zero in the case of this clock beingindicated by a double beat. The signal at X, therefore, wasmade at 9h 35m 558.45, and that of T at 9h 36m 58s.63. The rattle just preceding X was the signal that a star wasapproaching the transit wire. Fig. 153 is a representation ofa complete chronograph. 548. The Meridian Circle.—This has already been br

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1919

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