THE ARCH. 



123 



..V... 



mm^mmmm^mmii 



be far bettor, as well as much loss costly, for arches of 

 wide span. 



The vortical bond in a brick arch I have usually formed 

 in the following manner : Referring, for example, to a tunnel 

 arch of 13 foot radius and 1\ bricks in thickness, as shown 

 in the sketch, two special or radial bricks are required, 

 marked S 1 and S 2 on the sketch, in combination with 

 ordinary bricks, which we will take to be 9 inches long, 

 4^ inches broad, and 3 inches thick, with half-inch joints of 

 mortar. The size of S 1 would 

 be Oinclies long, G inches broad, 

 and tapering in thickness from 

 2 inches at the lower end to 2| 

 at tho top; that of S 2 being D 

 inches long, 5 inches broad, and 



tapering in thickness from 2| 

 to 3 inches at top. These 

 special bricks would be of the 

 same cubical contents as the 

 ordinary bricks, and could be 

 made in largo quantities for 

 hvo shillings a thousand extra. 



Referring once more to the 

 sketch, it may be observed 

 how the bricks are laid form- 

 ing a full half-brick vertical 

 bond, the mixture of common 

 and special bricks shown in 

 two courses of the sketch making together one block of 

 the brickwork (two such blocks are shown in the sketch) 

 exactly fitting the curvature of the arch, six common 

 bricks being used to every four specials ; and as a 

 thousand bricks will make three yards of brickwork, the 



