 161  THE AIR We live at the bottom of an ocean of a gas that we call air. Air is the gas which we know best, and, in discussing gases (1), we shall use it as an example. You must remember, however, that the laws that apply to air apply to all other gases. Air has weight. We can easily show it if we weigh an incandescent lamp. Heat a spot on the lamp red not (2), using a mouth blow-pipe (3). The air pressure will make a hole through the glass and the lamp will fill with air (4). weigh it again and you will find that the lamp weighs more than before, because it is now full of air. fill the lamp with water and find its volume. Now you have all the figures necessary to determine the weigh of one cubic foot of air. Thus we know that the weight of a cubic foot of air at О С (5) and 76-cm (6) pressure is .081 pound, or 12 cubic feet of air weigh a pound. Since air has weight, it must press down on the surface of the earth. At sea level the pressure of the air on the surface of the earth is about 15 pounds per square inch. We often call this pressure of 15 lb. per sq in (7) a pressure of one atmosphere, but the figure 15 is not exact because the pressure varies with the level of the place and the height of the barometer at the time. From Elements ofPhysics by Duff and Weed Приме' (1) in discussing gases - говоря о газах (обсуждая) (2) red hot - докраска (3) a mouth blow-pipe - паяльная трубка. Существительное mouth рот здесь упот еблено как определение (см. урок 5). (4) will ill with air - наполнится воздухом. Заметьте употребление ппрецога with. (5) at О С - 0 градусов по Цельсию. С - centigrade ['sentigreid] - стоградусный. (6) cm = centimetre - сантиметр (7) 15 lb. per sq in = fifteen pounds per square inch - пятнадцать фунтов на квадратный дюйм Сокращение lb. происходит от латинского слова libra фунт. Запомните сокращенные написания, встречающиеся в тексте. 161 |
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