STORAGE AND REGULATION OP WATER. XLVII. 



advances in science with regard to the stresses on dams, 

 would venture to state with confidence how much the 

 water might be raised in the reservoir." 



Sir William Garstin, Adviser to the Egyptian Ministry 

 on Public Works, writes as follows : — " Eventually it is to 

 be supposed that specialists will arrive at a conclusion 

 upon this most important theory, which affects all existing 

 dams, and which must influence all future designs for such 

 works." 



The whole subject is of course very abstruse, and can 

 only be shortly referred to here, leaving it to be amplified 

 by the discussion upon it, which must sooner or later take 

 place. A good idea of the matter may however be obtained 

 if we lay a number of books on top of each other to repre- 

 sent a dam, cut (theoretically) into horizontal layers. 

 Now, according to former dam practice, if these books 

 cannot be pushed asunder, nor the combined books turned 

 over, they will represent a stable dam. The new theory 

 says, turn the books on their edges, when this combined 

 book dam may fail first by a lifting of their lower edges at 

 the sides nearest the applied force and then by the resis- 

 tance to shearing, or the friction between the books being 

 overcome when they will fall down. 



It may be stated in mathematical form as follows : The 

 differential equation for dam strains can be made to consist 

 of two parts, viz. 



Tensional or pressural stress = p x + p 2 

 Shearing stress = Sx + 8 a 



when pt = pressure, as the strain varies, according to its 

 distance from the neutral axis 

 2>l — certain additional strains of positive or negative 



magnitudes 

 Si = the parabolic distribution of stress 

 S 2 = certain additional stresses of positive or negative 

 magnitude 



