A text-book of general astronomy : for colleges and scientific schools (1888)
Young, Charles A. (Charles Augustus), 1834-1908 · Boston ; London : Ginn & Company · leaf 486
ble-image prism D is so chosen that aa and be will benearly parallel to each other, and a suitable diaphragm1 E cuts off the twoother pencils ae and b0. A Nicol prism N receives the two pencils that comethrough the diaphragm, and the eye views the two images through the eye-piece at I. These… … Fig. 219. — Pickerings Meridian Photometer. at which the images will appear equal in brightness, whatever may be theoriginal ratio of brightness between the pole-star and the object observed.On looking into the instrument the observer sees two stars, the pole-star atrest, the other moving along as…
Astronomy
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