THE AECH. 



129 



necessary thickness of an abutment to carry the thrust of 

 any given arch. There, abutments are supposed to be built 

 of the required thickness according to the height, in ordi- 

 nary brickwork or masonry; the mass of the abutment 

 being sufficient to bear the thrust of the arch. The con- 

 sequence is, that the arch is always shoving at the abut- 

 ments, and there is nothing but the friction of the courses 

 to resist this action, with the result that where there is 

 much jar from heavy waggons passing along a street along- 

 side, such arches frequently settle and open at the joints 

 more or loss in the course of time. An instance may be 

 observed in tho fa^iade of the old station front built at 

 Temple Meads by Brunei years ago. It may be recollected 

 that an entrance and an exit archway were built at either 

 end of the facade— one under the clock which used to be 

 there, and the other, which has recently been pulled down 

 by the Tramway Company. Now these arches were only of 

 thirteen feet span and all the masonry was splendidly built 

 — a full thickness of abutment, according to rule, being 

 allowed to both arches; but I had noticed for years that 

 openings and settlements in tho joints of both of those 

 arches had taken place (tho worst being in that on the 

 tramway side). These settlements were caused gradually 

 by the jar of tho passing wagons on the street pitching. 

 Those on the clock side have been pointed over on the front 

 fafade, and aro somewhat hidden, but at the back they are 

 more visible. Now we can tell precisely the amount of 

 horizontal thrust of these arches against tho abutments ; 

 and if the abutments had been built with a certain amount 

 of countervailing hatter which was also loaded on the top, 

 thon one thrust might have been made to balance the other, 

 and there could have been no settlement of that sort. This 

 battering wall need not appear on the outside, for it may 



