ON ARCHITECTURE AND CARPENTRV. • l/I 



effect in diminishing its strength in resisting a longitudinal force; and this 

 diminution must be determined according to the principles that have been laid 

 down respecting the equilibrium of elastic substances. 



Wooden bridges, and the temporary centres on which arches of stone arc 

 supported during their construction, depend nearly on the same principles as 

 roofs: the external parts usually support a thrust, and the internal act as 

 ties; but the abutments are generally capable of withstanding a horizontal 

 thrust without inconvenience, so that by their assistance the strain on the 

 ties is considerably diminished. Great strength may also be obtained, where 

 it is practicable to support each part of the centre by two beams, in the di- 

 rection of chords, bearing immediately on the abutments. (Plate XIV. 

 Fig. 178, 179.) 



The various articles of household furniture belong to subordinate branches 

 of carpentry, but their form is in general more accommodated to conveni- 

 ence and elegance than to strength and durability. Yet even in making a 

 chair, there is room for error and for improvement ; the same principles that 

 direct us in framing a roof, are capable of application here; but if they were 

 implicitly followed, they would lead us to the employment of bars crossing 

 each other in an inelegant manner. Doors, gates, locks, and hinges, are 

 either parts of the carpenter's employment, or appendages to his works; and 

 it is possible that^by attentive consideration, improvements might be made in 

 all of them. Mr. Parker has devoted much time and labour to the subject of 

 gates, with their hinges and fastenings, and has presented to the Royal In- 

 stitution a very useful collection of models, which show the result of his in- 

 vestigations. 



