OX STJtAJN. 



Ibs. per square foot and estimated as being exerted upon 

 the vertical plane as projected through the centre of gravity 

 of a cylindrical structure; thus, to estimate the maximum 

 pressure of the wind exerted upon the semi-cylindrical sides 

 of a stand-pipe 20 ft. in diameter and 120 ft. in height, 

 20 X 120 X 30 Ibs. equals 72,000 Ibs. or 36 tons, and the 

 moment of this force, or the pressure in tons multiplied by 

 its leverage, or its distance from the centre of gravity about 

 the point, is 60 ft. X 36 tons, or 2, 160 ft. -tons. 



The resistance offered to this overturning moment is the 

 weight of the structure, in tons, multiplied by its leverage, 

 or its perpendicular distance from its centre of gravity at its 

 base to the point or toe, and as the centre of gravity of a 

 cylinder is the centre of the circle, the leverage is therefore 



FIG. 8. The pressure against a semi-cylindrical surface a b c n o m is about 

 ' one half that against the flat surface abnm. 



its radius, or in this case 10 ft., so that the moment of this 

 force is its weight, say 80 tons, multiplied by its lever-arm, 

 10 ft., or 800 ft. -tons, therefore the resultant of these two 

 moments shows an excess of 1360 ft. -tons, in amount and 

 tendency sufficient to render the structure unstable or to 

 cause its overturning. In order, therefore, to render such a 

 structure stable upon its foundations, it will be necessary to 

 provide a suitable anchorage. In order to show the instabil- 



