62. Brickwork is measured by the square rod of 30 square yards, or in round numbers 272 feet; in the North it is measured by the square yard. What in England, where brickwork is carried out to a much larger extent than it is in Scotland, is called the " standard" thickness, is 14-inch or brick-and-half work, a rod of which is equal to 306 cubic feet, or 111/5 cubic yards; this with the mortar, which on an average will make 71 feet, will give a weight of 15 tons. A cubic foot of brickwork weighing somewhere about from 100 lbs. to 1 cwt., according to the quality or density of the bricks; of stock bricks four courses high will take 4352 to make a rod, 4533 four courses high; the weight of a brick averages 5 lbs. The weight per cubic foot of machine-made bricks - Platts, 123.57; of another class, which is the highest of which we have a record, 118.75; of handmade bricks the lowest average gives 111'65 lbs. to the cubic foot, the highest 113.69. Of the above-named bricks, and in their order as given, the weight of water absorbed was 180.93 oz., 127.62, 150.29, and 144.6. The crushing weight of a brick, average hardness or density of the best quality, is nearly 1100 lbs.; that of an ordinary brick of poor quality may be taken at nearly 900 lbs. Of roofing or pan tiles the weight may be taken, on an average, of 5 lbs.; plain tiles 2 lbs.

63. The following give the proportions of the various peculiarities of different classes of "timber" as stiffness, elasticity, transverse strength, etc., according to the strains which we have already named. The first is the " stiffness," English oak being taken as the standard, and put down as 100: - American oak, 114; beech, 77; ash, 89; elm, 78 ; sycamore, 59; larch, 79; chestnut, 67; cedar, 28; Riga fir, 98; Memel fir, 114; Scotch fir, 55; white American spruce, 72; yellow pine, 95; pitch pine, 73; Honduras mahogany, 93; Spanish do., 92; walnut, 49; poplar, 44; teak, 126.