+------------+--------------+-------------+---------------+ | Wire | Weight | Wire | Weight | | Gauge. | Per Square | Gauge. | Per Square | | | Foot. | | Foot. | +------------+--------------+-------------+---------------+ | No. | Oz. | No. | Oz. | | 30 | 10 | 22 | 21 | | 29 | 11 | 21 | 24 | | 28 | 12 | 20 | 28 | | 27 | 14 | 19 | 33 | | 26 | 15 | 18 | 37 | | 25 | 16 | 17 | 43 | | 24 | 17 | 16 | 48 | | 23 | 19 | 14 | 60 | +------------+--------------+-------------+---------------+ QUALITIES OF DIFFERENT ROPES EXPRESSED RELATIVELY. +--------------+----------+-------------+--------+-------------+ | | Strength.| Rigidity. | Weight | | | | | | Dry. | Stretching. | +--------------+----------+-------------+--------+-------------+ | Italian Hemp | -- | 1 | 1 | } | | Baltic ” | 0·7 ·9 | 0·8 to 0·9 | 1 | }1/7 to 1/12| | Manilla ” | 0·9 to 1 | 0·75 | 0·88 | } | | Flax | 0·9 | low | -- | 1/75 | | Iron Wire | 3 | high | 4 | -- | | Steel | 6 | high | 4 | -- | +--------------+----------+-------------+--------+-------------+ Steel wire rope stretches about 1/360, 1/250, and 1/100, of 1/4, 1/3, and 1/2 the breaking weight. THE ATMOSPHERE. The composition of the atmosphere is by volume, oxygen 20·8, nitrogen 79·2; by weight, oxygen 23, nitrogen 77. There are also minute quantities of carbon dioxide, aqueous vapour, and ammonia. The barometer falls about ½” for each 500’ increase of altitude the mean temperature being 50° Fahr. WEIGHT OR PRESSURE. = 14·706 lbs. per square inch. = 29·92 inches of mercury. = 33·7 feet of water. SQUARES, CUBES, SQUARE ROOTS, AND CUBE ROOTS.