148 



SMALL WATER SUPPLIES. 



parallelogram DCEB. From the centre of gravity 

 of the wall set up a perpendicular cutting CD in F, 

 and from F set off FG equal to weight of wall and FH 

 equal to thrust at skewback. Now complete the 

 parallelogram FGJH. Combine this last resultant 

 FJ with the earth thrust and we have the new paral- 

 lelogram KLMN. Finally the resultant of this dia- 



FIG. 1 1 6. 



gram KM must be combined with the water thrust, 

 giving the figure OPQR. If this drawing has been 

 done accurately to a large scale, the distance d (ex- 

 plained before) may be measured with accuracy and 

 the intensity of stress found in the usual way by the 

 formula 



W M 

 ^ etc. 



