GB120755A - Improvements in Prismatic Telemeters. - Google Patents

Abstract

120,755. Ray, J .W. Nov. 10, 1917. Range - finders. - Apparatus for use in determining distances, or for enabling a constant distance to be maintained between ships, comprises a prism rotatably mounted in a ring, the ring being provided with a handle by which it may be held at arm's length with its plane vertical and also with a definite diameter vertical; in a modification, two similar prisms rotatable simultaneously and equally in opposite directions may be provided. As shown in Fig. 3, a prism D is carried by a bezel B which is provided with a handle and is rotatable in a ring A. The ring A is split at its lowest point, the ends being secured to a piece a<3> which has a screwed stem a<4> fitting into a handle C. A clamping-screw which passes through the piece a<3> and the ring A enables the bezel to be secured in any desired position. In use the instrument is held so that an object may be viewed directly and also through the prism, and the prism is adjusted so that a particular point on the object, as seen directly, is level with another particular point on the object, as seen through the prism, the prism being then clamped in position. Any change in the relative distance of the object will be indicated in later observations by variation in the relative levels of the points observed. If the distance between the points is known the distance of the object may be obtained by observing the angle through which the prism has been rotated and by use of a reference table. In the modification shown in Fig. 6, two prisms D, D' (shown in broken lines) are mounted in separate bevels B, B<1>, each having a ring of teeth b<5> engaged by a pinion b<6> attached to a milled wheel b'. As the milled wheel is turned, the prisms are rotated in opposite directions, the image being consequently displaced vertically without lateral displacement.