20S Report on the Progress and State of Applied Mechanics. 



divisions of Constettctioit and Mechanism, of which it consists when 

 regarded as an art. 



6. In the perfecting of Ai:)pUed Mechanics, whether as a science or as 

 an art, the end aimed at, and the criterion by which true is to be dis- 

 tinguished from false progress, may be expressed by the word Economy ; 

 that is, the production of every desired effect by those means which are 

 exactly adequate to produce it, and no more. Whether in structures or 

 in machines, the proportion borne by the means exactly adequate to 

 produce an effect, and the means actually employed, can be expressed by 

 numerical ratio. For peefect Economy, that ratio is Unity ; but 

 perfect economy never is, nor can be attained in human works ; and in 

 them the economy realized is expressed by some fraction, falling short 

 of unity by a quantity which expresses the ivaste of means. Theory 

 strives to ascertain, by experiment and by reasoning, the exact amount 

 and causes of waste, and how it is to be reduced; and practice strives, 

 by continually improving skill, to effect that reduction ; and both tend 

 to bring the fraction that denotes actual economy, continually nearer 

 and nearer to that unit, which expresses the unattainable, though not 

 unapproachable, limit of the result of human efforts. 



7. In a Structure three things are to be considered ; its materials, — 

 the mode of putting them together, — and the purposes for which the 

 structure is to be used. 



8. The materials of structures are inorganic and organic. Inorganic 

 materials are for the most part either stony or metallic. Organic ma- 

 terials are of vegetable or animal origin. 



9. With regard to natural stone, the chief improvements which have 

 of late years been made, have been in the art of separating it from its 

 native rock by blasting. Much skill is employed in the placing of 

 mines so as to detach large masses of it with the least possible waste 

 of powder and of stone ; and the heat generated by currents of electri- 

 city in metallic wires, has for many years been advantageously employed 

 to lire the charges at one instant. Some of the most remarkable 

 operations of this kind, of recent date, are described in a paper read by 

 Mr. Sim (manager of the granite quarries at Fui'nace) to the British 

 Association at Glasgow, in 1855. 



10. The transport of good building stone from a distance is a matter 

 of importance to those places where it is deficient. Thus, in those 

 pai'ts of the south of England where the formation is chalk, and the 

 only stones fit for building that are found on the spot are the flints 

 imbedded in the chalk, a valuable article of commerce is the oolite 

 which is imported from quarries in Normandy, and whicli though soft 

 when first quarried, and capable of taking the most delicate carving 



