THE CENTROID AND MOMENT OF INERTIA 257 



139. In dealing with irregular figures, the work is rendered much 

 simpler by adopting a tabular method of working, and this will 

 be seen by a consideration of the following example. The given 

 irregular figure (Fig. 81) is contained in a rectangle whose base 

 is 9 inches and height 6 inches. The figure is divided into 10 

 vertical strips each of breadth 0-9 inches, and 10 horizontal 

 strips each of breadth 0-6 inches. The mid-ordinates of these 

 strips have been measured, and are given in the tables below. 



(1) Working with the vertical strips ; 



The breadth of the strip b = 0-9 

 Then Area = 42-43 x 0-9 

 = 38-19 sq. in. 



__<M) 412-49 

 = ~2~ 42-43 



V OY = 



= 4-374 in. 



x (0-9) 2 x 412-49 



1059 cub. in. 



x 42-43 -f 



~l2~ 

 = 917-8 inch units 



5022-9 



