\Q6 LECTURE XIV. 



The Gothic architects appear to have been superior to tlie Greeks 

 in the mechanical arrangement of the parts of their edifices, so as to 

 produce the most advantageous effect in preserving the general equi- 

 librium. They made every essential member of their buildings a constituent 

 part of their system of ornament, and even those embellishments, which, by a 

 superficial observer, might be deemed useless or prejudicial, are frequently cal- 

 culated, either by their strength, or by their weight, to serve some beneficial 

 purposes. The pointed arch is not in all cases well calculated for equilibrium, 

 but when it has a pillar resting on its summit, it is exceedingly strong. 

 The most celebrated of modern architects have sometimes been less successful 

 than those of the middle ages ; and for want of paying sufficient attention to 

 mechanical principles, have conunitted such errors in their attempts to pro- 

 cure an equilibrium, as have been followed by the most mischievous conse- 

 quences. Examples of this might be pointed out in the bridges of our own 

 country, and the churches of others; but if we are masters of the true theory 

 of pressure, we shall be able to avoid similar errors, without examining the 

 particular circumstances which have occasioned these accidents. (Plate XII. 

 Fig. 165.) 



The principles of equilibrium, which are employed in architecture, are 

 equally applicable to many cases in carpentry; and where the work is princi- 

 pally calculated to Avithstand a thrust, there is little difference in the operation 

 of the forces concerned; but where a tie is introduced, that is, a piece which 

 resists principally by its cohesive strength, the parts often require to be ar- 

 ranged in a different manner. The general principle, that three forces, in 

 order to retain each other in equilibrium, must be proportional to the sides 

 of a triangle corresponding to their directions, is sufficient for determining 

 the distribution of pressure in almost all cases that can occur. The conclu- 

 sions which have been drawn from this principle, and from other similar con- 

 siderations, respecting the strength of materials, will also be of great use in 

 directing us how to determine the best forms for beams, rafters, and timbers 

 of all kinds, and how to arrange and connect them in the best manner with 

 each other. 



The employment of the cohesive strength of materials in carpentry intro- 

 duces a difficulty which scarcely exists in architecture. Tavo blocks, placed 



