. Machinery and processes of the industrial arts, and apparatus of the exact sciences. be revolved one hundred and eighty degrees on its pivot. The telescope1/ will now come into the position far observation, and the mirror M7will be that which will reflect the right-hand image to the eye. This isthe mirror which has been turned by the micrometer screw. When theimage as reflected by it is brought to the central line by turning the boxas before, the other image, now reflected from M, will be twice as far fromthe center as in the former case. By turning the tangent screw m, themirror M will firs
. Machinery and processes of the industrial arts, and apparatus of the exact sciences. be revolved one hundred and eighty degrees on its pivot. The telescope1/ will now come into the position far observation, and the mirror M7will be that which will reflect the right-hand image to the eye. This isthe mirror which has been turned by the micrometer screw. When theimage as reflected by it is brought to the central line by turning the boxas before, the other image, now reflected from M, will be twice as far fromthe center as in the former case. By turning the tangent screw m, themirror M will first come into parallelism with M7, when the appearanceof things will be the same as that first presented, and afterwards passingbeyond the position of parallelism, will bring the second image again tocoincide with the first. The dial of m will then show twice as large anangular movement as that of m; and this reading will be very nearlythe true parallax. That it needs a correction to make it quite true willappear from examining the accompanying diagrams, Figs. 128 and 129. Fie-. Second observation. Disregarding the angular form of the telescope, suppose the observerseye to be at E, and that the object O is seen in the line G E. Another TELEMETRICAL APPARATUS. 587 object 0, one meter distant from O, will be seen reflected from M; intliesame direction, while another image of O will be observed in that mirrorout of the center. When coincidence is established by turning M, therays from O reflected from the second mirror will follow the line C C mirror M will then have a new position, which may be representedby M. Eevolving the instrument, the left-hand image will be seen in M, thereflected ray taking the direction 0 E, the axis of the box having nowa position deviating from that which it had originally, by half the angleOCO. M will have to be brought to the position W in order toestablish parallelism anew between the mirrors, when the object O willbe seen in the direction
Size: 2118px × 1180px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, booksubjectmachinery, booksubjectscientificappa
