CHAPTER VIII. 



OF THE PRESSURE OF NON-ELASTIC FLUIDS UPON DYKES, EM- 

 BANKMENTS, OR OTHER OBSTACLES WHICH CONFINE THEM, 

 WHETHER THE OPPOSING MASS BE SLOPING, PERPENDICULAR 

 OR CURVED, AND THE STRUCTURE ITSELF BE MASONRY 

 OR OF LOOSE MATERIALS, HAVING THE SIDES ONLY FACED 

 WITH STONE. 



1. OF FLUID PRESSURE AGAINST MASONIC STRUCTURES. 



204. BEFORE we proceed to develope the theory of Floatation, and 

 to explain the method of weighing solid bodies by immersing them in, 

 or otherwise comparing them with liquids ; it is presumed that it will 

 not be considered out of place, to take a brief survey of the circum- 

 stances attending the pressure of non-elastic fluids, when exerted 

 against dykes or other obstacles, that may be opposed to the efforts 

 which they make to spread themselves. 



This is an interesting and important subject in the doctrine of 

 Hydraulic Architecture, and since the principles upon which it is 

 founded, depend in a great measure on Hydrostatic pressure, it cannot 

 properly be omitted in unfolding the elementary departments of the 

 Mechanics of Fluids, which come so directly before our view in what 

 is called level cutting in the practice of canal making. Every one 

 knows that in cutting a canal, no further excavation is required than 

 that which will hold the water at a given depth and breadth ; when 

 a bank is made on both sides with the earth excavated, the 'level sur- 

 face of the canal may be elevated above the natural surface of the 

 adjacent land, and in this case great part of the cost of excavation 

 will be saved. But when the canal is to be carried along wholly 

 within embankments, too much attention cannot be paid to the prin- 

 ciples of fluid pressure, if we would avoid unnecessary expense, and 

 at the same time complete the work with systematic regard to its 

 permanent durability ; this therefore is the object of the present 



