408 



REPORT 1872. 



sume the tracer to start from C, and the wheels R &c. to be at zero, then in 

 the passage from C to D varying revolutions would be put into these wheels 

 corresponding approximately with the length of their arcs about the centre N ; 



Kg. 6. 



VJ 



..-r„ 



then, on the arrival of the tracer at D, the ratio for the "rale" of trace between 

 I) and A wiU be established, viz. the proportion which Y D (4 inches) bears 

 to the 5-inch length of Q, equal four iifths of the motion which the tracer T 



but the distance D A is 5 inches, and therefore 



is about to make along D A 



