1102 Transactions of tsb American Institute. 



of an incli ; or a vernier scale may be substituted for the index when 

 greater nicety is required. Any desired position of C may be 

 obtained by the set-screw, G, the head of which runs in a rabbeted 

 groove in the edge of the base board, A. 



H, the truck for the plan-board is provided with a guide index and 

 a set-screw as in the case, C. 



Upon this truck are erected two uprights or posts, I, joined at the 

 top and made firm by the cross-bar, J. These posts, as sho'wn at K, 

 are grooved, in which the tongues of the strong frame, L, have a free 

 perpendicular motion ; holding it at any desired point, indicated by 

 the index, M, on the scale, jST, by a set-screw on the back side, and not 

 shown in the diagram. 



Upon the frame, L, are fastened two guides, O, in which the plan- 

 board P, has a free horizontal motion, its position being indicated by 

 the index, Q, upon the scrole, R. The center, S, of the plan-board, as 

 shown by the dotted line, may be removed at pleasure by turning two 

 small buttons, so arranged as to be flush with the back, and oflfering 

 no obstacle to the proper motions. When the portion, S, is removed 

 a negative may be inserted in its place, and the aj^paratus is excellently 

 adapted to the production of glass positives, and is so used by me in 

 preference to a far more expensive apparatus which I constructed 

 sev^eral years ago expressly for such work. For convenience of 

 packing, laying away on the shelf, or hanging on a nail in the opera- 

 ting room, the uprights may be hinged as shown at T, allowing the 

 plan-board, when not in use, to fall forward, and lay flat uj)on the 

 base, A ; and when in use may be held in position by hook braces as 

 shown at U. The one which I use in my own practice is so 

 constructed. 



With this simple and cheap apparatus, many perplexities ma}^ be 

 avoided, and much time saved. The operator is always sure that the 

 plane of his original on the plan-board is at a true right angle with 

 the axis of his copying lens. The vertical or lateral position of the 

 original may be easil/ changed without interfering with the focus or 

 removal from the plan -board. i 



Whenever a copy of any special size is made, either equal, reduced, 

 or enlarged, and the positions of the several parts of the plan-board 

 and camera are noted, no further focusing upon the ground glass is 

 ever needed for reproductions upon that scale and by that lens. Of 

 course it is necessary to observe the position occupied by the ground 

 glass, for any given scale of enlargement, or reduction. A paper 



