A manual of spherical and practical astronomy, embracing the general problems of spherical astronomy, the special applications to nautical astronomy, and the theory and use of fixed and portable astronomical instruments, with an appendix on the method of least squares . to the right will be reflected into coincidence with the directobject, and the angular distance of the two objects is given bythe reading corrected for the index error. When the centralmirror becomes nearly perpendicular to the line Mm, the prismintercepts the rays from the right hand object. This occurswhen the angular distanc
A manual of spherical and practical astronomy, embracing the general problems of spherical astronomy, the special applications to nautical astronomy, and the theory and use of fixed and portable astronomical instruments, with an appendix on the method of least squares . to the right will be reflected into coincidence with the directobject, and the angular distance of the two objects is given bythe reading corrected for the index error. When the centralmirror becomes nearly perpendicular to the line Mm, the prismintercepts the rays from the right hand object. This occurswhen the angular distance of the two objects is about 130°.Beyond this point the head of tlie observer also intercepts therays, until we come to the position of Fig. 34. In this position two objects 180° apart can be brought intooptical coincidence. But, although the prism does not interferewith the rays from the second object, the head of the observermay; and this is obviated by placing a small prism D at the eyeend of the telescope, to reflect the two images which are incoincidence, to the eye in the direction DE. PRISMATIC CIRCLE. 129 Continuing the motion of the index, we see, by Fig. 35, thatangles greater than 180° can now be obtained until the indexarm comes against the prism
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Keywords: ., bookcentury1800, bookdecade1, booksubjectastronomicalinstruments
