Report on the Progress and State of Applied Mechanics. 209 



from carpenters' tools, hardens by exposure to the air, so as to become 

 strong and dm-able. The beautiful parish churches of Kent and Sussex, 

 in whose walls a concrete of flints fills the intervals between the carved 

 stone quoins and arches, show that at an early date the Normans imported 

 the stone of their province into the south of England ; but that impor- 

 tation ceased for a long time, and has only been of late years revived. 



11. Of Artificial Stones, the most useful, though not the most costly, 

 are bbicks. The art of making bricks, of regular figure and gi-eat 

 strength and durabiUty, was brought to great perfection by the Eomans, 

 and subsequently to their time it appears to have been much neglected 

 and forgotten, until of late years skill has been devoted to it with much 

 success. Bricks have been moulded by hand or by mechanism, of various, 

 convenient, and ornamental shapes ; they have been made of great 

 strength and accuracy of figure, by compressing dry clay ; but the most 

 useful improvements are those which have been made in the strength 

 and durability of common bricks, by good materials and careful work- 

 manship ; and of this some of the most remarkable examples are to be 

 found in Glasgow and its neighbourhood, where the frequent occurrence 

 of large and lofty structures of brick, and especially of furnace chimneys, 

 (one of which, that of St. RoUox, is, with three exceptions, the highest 

 building in the world), renders strength and durability absolutely ne- 

 cessary in bricks. 



12. Connected with the manufacture of bricks, is that of clay and 

 earthenware ptijies, for drainage and water-supply; an art of recent 

 origin, and very beneficial, by its enabling small channels for the con- 

 veyance of water, to be executed at a cost proportionate to their size. 



13. Amongst artificial stones may be classed viorta^-s and cements; 

 and of these the most important are such as harden readily in a moist 

 atmosphere, and under water. Hydraulic Limes and Cements, as they 

 are called, though much used by the ancients, especially the Romans, 

 were in former times comparatively rare and costly, because the quantity 

 in which they could be produced depended on the finding of certain 

 natural stones ; but now the researches of Pasley and Vicat have fur- 

 nished us with the means of producing artificially, by the combination 

 of lime with silica and alumina, or with oxide of ii'on, in proper pro- 

 portions, hydraulic mortar and cement in any quantity that may be 

 required. 



14. One of the most useful artificial stones is concrete: a mixture of 

 lime with gravel, and with fragments of stone. Though much employed 

 by the Romans, and by Mediaeval builders, its proper composition and 

 use appear to have fallen for a time into neglect, until of late years it 

 again received the attention of engineers. The great sea-wall at 



Vol. IV.— No. 1. 2 e 



