REPORT FOR 1897-PART II. APPENDIX NO. 10.

721

is completely withdrawn when mailing an exposure of the plate. B — graduated métal frame permanently flxed to the rear end of the caméra box G.

We will now describe how the plate holder is attached to the caméra for exposing a plate:

Frame II is set free from frame I, and K is hung to the frame II by means of the bent plate l, fig. 109, when the beveled projecting edge of K closes into the rebate of frame J/, producing a light-tight connection. K is now secured to frame 11 by the upper left and lower right hooks (Avhicli is the position shown in fig. 109). The hard-rubber slide S is now withdrawn, and the pair of hooks— upper right and lower left—are tightened to draw the holder K forward until the sensitive film surface is brought into contact with the graduated métal frame B at the back of the caméra C, the springs /taking up any lost motion and insuring a perfect contact.

The lens is now uncapped, the exposure made, and the plate holder is withdrawn by repeating the same operations in the inverse order: unfastening the pair of hooks—upper right and lower left— inserting the slide S, and drawing back the last two hooks—lower right and upper left.

(8) Captain HübVsplane-tablephotogrammeter.—This instrument is made by E. Lechner in Yienna, Austria, and it has been described in “ Lechner’s Mittheilungen aus dem Giebiete der Photographie und Kartographie,” Yerlag von E. Lechner (Wilhelm Millier) Graben 31, Wien.

The resuit aimed at in topography generally being the graphie représentation of the terrene, Captain Hübl replaced the théodolite of the ordinary photogrammeter by a plane table with alidade, thus being enabled to plat the directions required for the orientation of the picture traces, as well as those needed for the location of the caméra stations, directly in the field upon the plane table.

For this purpose the top M, fig. 112, of the caméra G, (21 by 21 centimètres) is disposed for use as a plane table. It receives the paper sheet, which is held in position by four métal corner clamps n.

Fig. 113 shows the plane table (or upper surface of the caméra) a b ed, which has two pivots, z and z1, about which the ruler LL of the alidade K may be revolved in azimuth. If zf, fig. 113, represents the constant focal length, eg will be the horizontal projection of the picture trace. By

placing the ruler LL of the alidade upon the pivot z the horizontal projections of horizontal directions emanating from z (representing the platted station point) as a center to those points of the perspective which serve to orient the picture may be drawn upon the paper between the sector e z g.

The central pivot fig. 113, serves as the vertical axis of rotation for the alidade ruler LL when drawing the horizontal directions to known points (signais over trigonométrie stations, visible from the caméra station) to locate the position of the station The line zf or z'f represents the horizontal projection of the principal ray (or of the optical axis of the caméra). It is the trace of the principal plane upon the horizontal-projection plane.

With reference to fig. 112:

c = caméra box made of aluminum, with constant focal length. It = plane-table alidade, arranged for stadia reading, with vertical circle. « = pivot over second nodal point of the caméra lens. z1 = pivot vertically above center of instrument (in prolongation of the vertical axis of rotation for the caméra or plane-table).

6581----40



Fig. 113

with' reference to surrounding triangulation points.

J*

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La langue de reconnaissance de l'OCR est le Français.

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