g-2 Description of a Flough-ettt. 



Away, and there would have remained another wedge 

 to k bar, which, as I observed before, in speaking of thtr 

 principle in regard to the construction of the ear, would 

 txbibit the moat ptrfcci i'oTm, were the only object to raise 

 the sod ; but as it must also be turned over, the kft half of 

 the upper wedge has been preserved, in order to eonlinue,on 

 the same side, the bevel to be formed on 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 trace out 

 lines around the block before we renvoved the pyramiiJ 

 (fiof. 4.) . Care must be taken not tr> confound these lines, 

 now that, they are separated by the vacuity left by the sup- 

 pression of that jivramid (6g. 5.). Make the saw enter in 

 the two points of the first line, situated at the places where 

 €he latter is interrupted, and which are the two points 

 where it is intersected by the external diagonals ok and m k, 

 continuing the stroke on that first line till it reach on the 

 one hand the central diagonal k /, and on the other the lower 

 right edge oh of the block (fig. 3.) : the posterior end of 

 {he saw will eome out at some point situated on the upper 

 trace in a straight line with the corresponding points of the 

 QilfTc and the central diagonal. Continue to do the same 

 thin"' on aH the pointa formed by the intersection of the 

 exterior diagonals and lines traced out around the block, 

 taking always the central diagonal, and the edge oh as the 

 term, and the traces as director,'* : the result wilr be, that 

 when you have formed several cnta with the saw, the end 

 of that instrument, which came out before at the vipper 

 face of the block, will come out at the face situated on the 

 left of the latter ; and all these difterent cnts of the saw will 

 have marked out as many straight lines, which extending 

 from the lower edge o A of the bk)ck, will proceed to cut 

 the central' diagonal. Now by the help of any proper tool 

 remove the sawn parts, taking care to leave visible the traces 

 of ihe saw, and this face of the ear wili be finished*. The 



trace* 



* The figures 9 and 10, which we have added here to thx)se which ac- 

 Gompimv Mr. Jefferson's memoir, were drawn in perspective by M. Valen- 

 cienne, assistant natiwalist belonging to the museum, and may serve to give 

 a better idea of the result of the operation here descrlfied. Let us suppose 

 that the s.iw cuts the lines 7nk, o k (ttg. i>.) in the points .t and t, taken ia 

 the traces x^ and ts situated ia (he same plane parallel to hare, and th& 

 prolongations of vhich on the trian;^!es m k I and o k I arc the lines a z and 

 t z ; the saw must then penetrare the block remaining- in the plane in ques- 

 tion until ils edge has arrived at the point s, and at tJie same time touch the 

 point z of the central diagonal k I. 1'he same edge of tlie saw will come OUl 

 at some point 1/ of the face ;n k I; io that the three jiolTits s, z, y., v/iU be ifef 



the 



