SO TOWERS AND TANKS FOR WATER- WORKS. 



of the external force to cut in twain or to shear the fibres, 

 and is the application of the forces in vertical planes at right 

 angles to the fibres, or through the cross-section of the body. 



The consideration and understanding of these stresses in 

 the material and members of such structures as towers, tanks, 

 and the like, and a knowledge of the resistance which the 

 character of the material, its dimensions, and shape, will offer 

 in opposition to extraneous forces is of the utmost im- 

 portance. 



The manner or method of the application of force to a 

 body necessarily comprehends a principle of mechanics known 

 as the "moment" of forces, or the tendency of a force to 

 produce motion about a point. This is an expression repre- 

 senting the power produced by the force to cause motion 

 about a point when acting through the principle of "lever- 

 age." 



In the consideration of the stability of a structure or its 

 ability to resist a sliding, horizontal motion, or a tendency, to 

 overturn about its toe, the consideration and application of 

 the principles of " leverage," and the opposing force exerted 

 by the natural law of gravitation, must be carefully analyzed 

 and observed. 



Moment of Forces. The ' ' moment " of a force is the prod- 

 uct of the force by its leverage ; thus, if the force or pres- 

 sure be represented by pounds, tons, etc., and the leverage 

 of the force, or the perpendicular or shortest distance from 

 its "fulcrum" to the direction through which the force is 

 acting is expressed in feet, this product is termed the 

 " moment " of the force about the given point, and may be 

 expressed as " foot-pounds " or " foot-tons." 



If any force, as 10 pounds, 10 tons, etc., be exerted 

 through a leverage of any number of feet, say 20, the result- 

 ant, 10 X 20 equals 200 feet-pounds or feet-tons. 



The resistance which the weight of a structure, acting ver- 



