379 



OBSTACLES IN CHAINING LINKS. (i). If the obstacle can be 

 seen over : Erect two perpendiculars (A C and B D) of equal length 

 at A and B ; then C D = A B. 



(2). If the obstacle cannot be seen over : Lay off A C and E F, 

 equal to one another, and at right angles to A F ; range the points 

 D and H in line with E C, and set off B D and H G at right angles 

 to E H, and each = E F or C A ; then C D = A B, and B and G 

 are points for ranging the continuation of F A. 



To MEASURE THE AREA, WHERE BOUNDARY IRREGULAR. 

 Lay off a base line, A G, and measure offsets to the various bends 

 and angles of the boundary line, and at right angles to the base : 

 this divides the enclosed space into approximate triangles and 

 trapezoids. The area of the triangles is calculated in the usual 

 way ; for the trapezoids the average of the two sides is taken and 



multiplied by the base : thus, area B C J H = B H 2 CJ x B C ; and 

 similarly for the rest : the sum of the whole= area A G M K H. 

 McConnelVs Xote Book. 



MISCELLANEOUS. 



Weight of F lough Harness. 



Collar 



Haims, iron-plated and straps 



Bridle 4^ 



Backband V 



Chains 8" 



15 Ibs. 



Total 38 Ibs. 



A bricklayer's hod carries 16 bricks, or \ bushel of mortar, or 

 f cub. feet. 



