Cj)£ 3irrlj. 



By CHARLES RICHARDSON. 



A paper read before the Engineering Section of the Bristol 

 Naturalids Society, on the 18th of October, 1887. 



"TTTHEN speaking of arclies, Dr. Huttoia says: "A large 

 ' V and elegant bridge, forming a way over a broad and 

 rapid river, is justly esteemed one of the noblest structures 

 that the skill of man can raise." 



I hat arches are naturally picturesqtie structures we may 

 infer from the fact that all artists bring a hridge into their 

 landscape whenever they can ; wo may therefore under- 

 stand that the Doctor's assertion is fully borne oat when 

 the bridge is both " large and elegant," but an arch cannot 

 be elegant that is not in accord with the true balance of 

 natural forces. 



Arches have been built for many centuries ; but the cal- 

 culation needed to ascertain their true form, with a full 

 knowledge of the pressures and thrusts at every jjoint, in- 

 volves the higher mathematics, which were only first dis- 

 covered in the time of Newton. Before that, therefore, the 

 building of arches must have been a mere question of trial 

 and ciTor, and subsequently of iade combined with prece- 

 dent. For instance, in our old Gothic architecture we have 



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