120 WELLS'S NATURAL PHILOSOPHY. 



_ 272. A PILE, in architecture and engineei- 



Whatisapile? . . t i p i 



ing, IS a cylinder of wood or metal pointed at 

 one extremity, and driven forcibly into the earth, to serve 

 as a support or foundation of some structure. It is gen- 

 erally used in marshy or wet places, where a stable found- 

 ation could not otherwise be obtained. 



,„, . In constructing columns for the support of the various parts 



ii.nns support- of a building, or of great weights, thej are made smaller at 

 1 'f-^er ^T^t'he *^® *'*^P *'''^° ^* ^^^^ bottom, because the lower part of the 

 b'lttnm than column must sustain not only the weight of the superior part, 

 "^ °^ but also the weight which presses equally on the whole 



column. Therefore the thickness of the column should gradually decrease 

 from bottom to top. 



What is an 273. An ARCH is a concave or hollow struct- 

 arch? ^^j.g^ generally of stone or brick, sui^ported by 

 its own curve. 



The base of an arch is supported by the support upon which it rests, while 

 all the other parts constituting the curve are sustained in their positions by 

 their mutual pressure, and by the adhesion of the cement interposed between 

 their surfaces. 



A continued arch is termed a vault. 



.„, . , An arch is capable of resisting a much greater amount of 



Why is anarch , , . , , 



stronger than pressure than a horizontal or rectangular structure constructed 



a horizontal qJ- ^j^g same materials, because the arrangement of the mate- 

 structure ? , 

 rials composmg the arch is such, that the force which would 



break a horizontal beam or structure is made to compress all the particles of 



the arch alike, and they are therefore in no danger of being torn or overcome 



separately. 



2H- The vertical wall which sustains the base of an arch 



abutment? 13 termed an abutment: when there are two contiguous 



arches, the intermediate supporting wall is called a pier. 



A beautiful application of the principles of the arch exists 



lustrations of ^ the human skull, protecting the brain. The materials are 



the principles jjej-e arranged in such a way as to aftbrd the greatest strength 



with the least weight. The sliell of an egg is constructed 



upon the principle of the arch ; and it is almost impossible to break an egg 



with the hands, by pressing directly upon its ends. A thin watch-glass, lor 



the same reason, sustains great pressure. A dished or arched wheel of a 



carriage is many times stronger to resist all kinds of shocks than a perfectly 



flat wheel. A full cask may fall without damage, when a strong square box 



would be dashed to pieces. 



What is an 275. By an order in architecture we under- 



order in archi- , -t .• ij? • ii 



lecture? Stand a certain mode oi arranging and decor- 



