The frame on which the photograph
The frame on which the photograph
are noneffecti?e in that conditio First as regards direct reduction; two extreme positions are indicated in Fig 1 and 2.is is set, P that on which the zinc plate is clamped; they both run on parallel tramways, shown by the dotted line C A B is a bar turning The minor details connected with this part of the machinery are as follows:The handles H are used for clamping purposes; they are the long arms of levers, which, when pushed perpendicularly to the limb, squeeze powerfully by means of the bluntly curved heads of their short armThe shaded square on P is the zinc plate, on which the reduction is made ; this is clamped by two handles on to a brass slide, which is slid into grooves in P, and there clamped fast by the screw, whose head is seen in Fig. 9. The six milled heads on Q are screws with projecting flanges, to nip and hold firmly a long deal board, to which the photograph has been securely pinneAs regards the upper stage, Fig. 10, which carries the pointer M, and the style or drill N, it consists of two brass bars sliding in solid iron cheeks ; the bars are connected together by links on precisely the same principle as those already describeThe link work is necessarily hidden in Fig. 10, but the position of the sliding centres is easily to be guessed; the link work is better seen in the perspective view,The three pegs to fix this part of the instrument, when adjusting, are shown at G. In connection with the framework which carries the pointer R, there are several matters of detail, as follow A second pointer will be observed outside the arm; and it will be seen that the line connecting the two pointers is always parallel to the tramways; the use of the two pointers is to enable the operator to set the board to which the photograph is pinned in such a way, before it is clamped to Q, that the fiducial line of the photograph shall be truly parallel to the tramway For, if when one point of the line is brought under M, and another point is brought under the second pointer, and the board be clamped in that position, the required object is attaine The framework that carries the pointers can be moved at will along the arm on which it is set by turning a milled head, the line connecting the two pointers always.
