. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. n,round whose edge the cloth passes, and which renders it vertical. The piece is kept intension crosswise by small brass templets, to which the strings g are attached, and bywhich it is pulled towards the sides of the frame f. It remains to show by what ingeni-ous means this frame may be shifted in every possible direction. M. Heilmann has em-ployed for this purpose the pantograph which draughtsmen use for reducing or enlargingtheir plans in determinate proportions. b b fb {fig. 371
. A dictionary of arts, manufactures and mines : containing a clear exposition of their principles and practice. n,round whose edge the cloth passes, and which renders it vertical. The piece is kept intension crosswise by small brass templets, to which the strings g are attached, and bywhich it is pulled towards the sides of the frame f. It remains to show by what ingeni-ous means this frame may be shifted in every possible direction. M. Heilmann has em-ployed for this purpose the pantograph which draughtsmen use for reducing or enlargingtheir plans in determinate proportions. b b fb {fig. 371) represents a parallelogram of which the four angles b b,fb, arejointed in such a way that they may become very acute or very obtuse at pleasure,while the sides of course continue of the same length ; the sides b, b and b, b are pro-longed, the one to the point d, and the other to the point c, and these points c and rf, EMBROIDERY. 437 are chosen under the condition that in one of the positions of the parallelogram, theline c d which joins them passes through the point /; this condition may be fulfilled in. an infinite number of manners, since the position of the parallelogram remaining thesame, we see that if we wished to shift the point d further from the point b, it wouldbe sufficient to bring the point c near enough to b, or vice versa; but when wehave once fixed upon the distance b d, it is evident that the distance b c is its necessaryconsequence. Now the principle upon which the construction of the pantograph restsis this; it is sufficient that the three points d, f, and c be in a straight line, in one onlyof the positions of tlie parallelogram, in order that they shall remain always in a straightline in every position which can possibly be given to it. We see in the figure that the side b c, has a handle b with which the workmanputs the machine in action. To obtain more precision and solidity in work, the sidesof the pantograph are joined, so that the middle of their t
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Keywords: ., bookcentury1800, bookdecade1840, booksubje, booksubjecttechnology
