171 



and tread being determined, the limb is then arranged on the mem • 

 bers of the square to correspond therewith, and the instrument thus 

 arranged being applied to the plank from which the carriage is to be 

 cut, the members of the square will give the scribing edge required 

 for the saw. 



To explain more clearly the practical operation of this instrument, 

 we will suppose that the length and mitre of a brace is required, 

 where the perpendicular bearing is ten (10) feet, and the horizontal 

 footing is six (6) feet, all that is required in this case is to place the 

 zero point of the moveable limb at ten (10) on the long member of 

 the square, causing the graduated edge of the limb to intersect the 

 graduated edge of the other member of the square at six (6), when 

 the length of brace required may be found by the reading on the 

 limb at the point of intersection, which will give, as the required 

 length of brace, eleven (11) feet eight (8) inches. And, upon secur- 

 ing the moveable limb to the members of the square, by the thumb- 

 screws, and applying the edge of the moveable limb to the side of 

 scantling, the members of the square will give a scribing edge for the 

 two mitres desired. 



The sum of the squares of the two sides of a right angled triangle 

 is equal to the square of the hypotheneuse. 



102 ^ 100 

 62 = 36 



136 (11.66 = 11 feet 8 inches. 

 1 



21)36 



226)1500 

 1356 



2326)14400 

 13956 



A coin of aluminum was offered for the inspection of the 

 members by Mr. Du Bois, accompanied by a communication 

 on the subject. 



