A B C OF THE STEEL SQUARE 113 



For a three by four foot run, take 12 inches 

 on the tongue and 9 inches on the blade, and 

 apply four times, because, as three feet is % of 

 four feet, so 9 inches is % of 12 inches. 



A young carpenter, Toronto, wants to know 

 how to find the center of a circle by aid of the 

 Square. 



Fig. 76. 



Answer: In Fig. 76 is shown how the center 

 of a circle may be determined without the use 

 of compasses ; this is based on the principle that 

 a circle can be drawn through any three points 

 that are not actually in a straight line. Sup- 

 pose we take A, B, C, D for four given points, 

 then draw a line from A to D, and from B to C : 



