INStRUMENT FOR REDUCINO OR ENLARGING PLANS* IJQ 



^hattheautbor merits theencpuragementofthe class, and pro- 

 pose, that its approbation should be given to the machine. 



IV. 



Description of an Instrument for facilitating the Reduction 

 of Plans; by Mr, de la Chabkaussiere*. 



HAVE thought of an instrument for reducing plans, Simple instru- 

 ^ ment for re- 



I 



which is so simple, that I am surprised it was not invented ducine"plaris. 

 by others long ago: bflt this simplicity, which I consider as 

 an advantage, is probably the reason, I call it a minudo^ 

 meter, as its principal object is the reduction of plans; 

 though it will answer equally well for enlarging them. 



This instrument is a wooden rule, with fiducial edges, atTheminudo- 

 the extremity of which is a pivot; or a plate of metal with a J"^'t,^'ji *" 

 hole, into which a pivot may be inserted at pleasure. This 

 pivot is a piece of a needle, with a knob for a head, 

 . On this rule are marked two scales, one smaller than the 

 btTier in any proportion you please. As my purpose in 

 making it was chiefly for plans of mines, I took as a basis a Particulailj 

 scale of 3 lines to a fathom, the proportion generally used pjansofminw 

 for such plans; and for the reduction I employed a scale of 

 one line to a fathom. Such a scale diminishing the length 

 and breadth of a plan two thirds each, all the parts will be 

 brought sufficiently near to be considered at one view. Such 

 a plan may be inferior in minuteness of detail and accu- 

 racy to a larger, but it has the advantage of being more 

 portable, and will enable the manager to have a clear idea 

 of the works under his direction. 



Suppose then I would reducea plan of three lines to the fa- Method of 

 thorn to a third of this in all its dimensions. I take a rule of inmum«nt 

 two feet long, which appears to me the most suitable length, 

 and divide it into three parts, which makes eight inches, or 

 96 lines [of course in English measure 80 lines] to each part. 

 On the first division, reckoning from the pivot, I trace the 

 little scale of one line to a fathom, which giv« me 96. 

 From the extremity of the small scale I begin the divisioa 



•Journal des Mines, Vol. XXVI, p. 461, Exuacted from a paper 

 sent to the Council of Mines. 



N« of 



