HISTORICAL SKETCH OF VAULTS.

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Science is useful to an architect only as it rendersthe application of his means more convenient andless expensive. Projecting for an immediate object,it seldom leaves in its productions the properties ofconversion : though it may make the architect bold,that boldness is displayed by the weakness of hisstructure, or in its being only sufficiently strong. Ithas been before shewn, that the science displayed ina building may be estimated by the inverse ratio ofthe quantity of materials : on the other hand, it oftenhappens, that the strength in a building may be esti-mated by an inverse ratio of the science in the con-struction. The maximum of skill was shewn by theItalian, whose edifice was so duly balanced, that itwould fall by a sparrow perching on any part of it.The Egyptian and Greek, alike unacquainted withthe due adjustment of forces, in the ample pi’ovisionsuggested by their cautious ignorance, in a kind ofporism unknowingly secured their buildings againsttime and violence. He who calculates powers, oftenforgets that his formulae are not applicable to thoseenemies to buildings ; and that the uncertain data ofdecay and popular frenzy cannot be mixed with thecertain data of gravitation.

M. Bossut, in his Traite de Mechanique, observes,that it does not appear that the ancient architectswere guided by certain and geometrical principles inthe means which they adopted to secure the stabilityof their edifices. Experience, imitation, and a naturalknowledge of mechanics, served them as their guides.Vitruvius , who has treated on all the subjects whichappeared to him to have any relation to architecture,has been wholly silent in respect to the advantage tobe obtained from mechanics, in acquiring a knowledge