The first operation consists in forming this tail by sawing the block (Fig. 2.) across from a to b on its left side, and at the distance of 12 inches from the end f then continue the notch perpendicularly along b c till within an inch and a half of its right side ; then taking d i and e h, each equal 11 inch, make a mark with the saw along the line d r, parallel to the right side. The pieceabcdefg will fall of itself, and leave the tail k, an inch and a half in thickness. It is of the anterior part a b c k l in a of the block that the ear must be formed.
By means of a square, trace out on all the faces of the block lines at an inch distance from each other, or which there will necessarily be 23: then draw the diagonals X. in (Fig. 3.) on the upper lace, and k a on that which is situated on the right; make the saw enter at the point nt, directing it towards k, and making it descend along the line in I until it mark out a straight line between k and / (Fig. 5.); then make the saw enter at the point o, and, preserving the direction a k, make it descend along the line o / until it meet with the central diagonal k I, which had been formed by the first cut: the pyramid k nt 71 a I (Fig. •.) will fall of itself, and lease the block in the form represented by Fig. 5.
It is here to be observed, that in the last operation, in stead of stopping the saw at the central diagonal k I, if we had continued to notch the block, keeping on the same plane, the wedge I n a k b (Fig. 3.) would have been taken away, and there would have remained ano ther wedge lakbar, which, as I observed before, in speaking of the principle in regard to the construction of the ear, would exhibit the most perfect berm, were the only object to raise the sod ; but as it must also be turned over, the left half of the upper wedge has been preserved, in order to continue, on the same side, the bevel to be formed oil the right half of the lower wedge.
Let us now proceed to the means of producing this bevel; in order to obtain which, we had the precaution to Dace out lines around the block before we removed the pyramid (Fig. 4.). Care must be taken not to con found these lines, now that they arc separated by the vacuity left by the suppression of that pyramid (Fig. 5.) Make the saw enter in the two points of the first line, situated at the places where the latter is interrupted, and which are the two points where it is intersected by the external diagonals o k and in k, continuing the stroke on that first line till it reach on the one hand the central diagonal k 1, and on the other the lower right edge a h, of the block (Fig. 5.): the posterior end of the saw will
come out at some point situated on the upper trace in a straight line with the corresponding points of the c dge and the central diagonal. Continue to do the same thing on all the points formed by the intersection of the exte rior diagonals and lines traced out around the block. taking always the central diagonal, and the edge a h as the term, and the traces as direr tors: the result w ill be, that when you has e formed sus el al cuts with the saw, the end of that instrument, which came out before at the upper face of the block, will come out at the race situ ated on the left of the latter; and all these dilIerent cuts of the saw will have marked out as many straight lines, which, extending the lower edge o of the block, will proceed to cut the central diagonal. Now by the help of ally proper tool, remove the Sian] parts, taking care to leaNe visible the traces of the saw, and this face of the car will be finished.` The traces will serve to Silo• lio• tile wedge which is at the right angle rises gradually on the direct or lower lace of the wedge, the inclination of which is preserved in the central dia gonal. (inc may easily conceke and render sensible the manner ill N\ filch the sod is raised On the ear, which we have described, by Ira( ing out on the ground a pa rallelogram two feet long and nine inches broad, as a b o d (Fig. 6.): then plat ing in the point b the end of a stick 27,' inches in length, and raising the other end 1 2 inches ;Wove the point c; (the line i/ e, equal to 4. inches, re presents the quantity which the height of the car e:t ceeds the pcipzudicidar.) this is done, take ano ther stick 12 niches in length, and, placing it on a b, make it move backwards, and parallel to itself from a b to c d, taking care to keep one of its ends always on the line a d ; while the other end moves along the stick which here represents the central diagonal. The mo tion of this stick of I2 inches in length ‘1 ill be that of our ascending- wedge, and NS ill show how each trans verse line of the sod is carried from its first horizontal position until it be raised to a height which exceeds the perpendicular so much as to make it Lill inverted by it own w eight.