Английский язык в сфере профессиональной коммуникации: природопользование - 15 стр.

oxygen and nitrogen. There are about 21 parts of oxygen and 79 parts
of nitrogen.
       Men and nearly all animals must have oxygen or they cannot
live. In the atmosphere there is also a little carbon dioxide. Now plants,
trees, grass cannot live without carbon dioxide. Besides oxygen,
nitrogen and carbon dioxide there are small quantities of other gases
in the atmosphere; by far the most important is moisture or water
vapour. The atmosphere has thickness at least 80 kilometers but the
upper layers are pressing down on the lower layers, so the air there
is much denser and heavier while in the upper layers it is thin or
«rarefied».
       Whatever you do, a column of air at least 80 kilometers high is
pressing down upon you. Although you do not feel it, this column of
air is exerting a pressure equal to 73,2 kg on every square meter of
your body. People who climb high mountains where the air is thin
find it very difficult to live and breathe. On the top of Mount Everest
(8848 metres) the pressure is much less than one-fifth the one at
sea-level and it is almost impossible to live at such a height even for
a short time. Even at the sea-level the pressure is not the same at all
places.
       Nevertheless the composition of the air varies slightly with
elevation, being a little richer in oxygen and poorer in nitrogen at sea
level than at elevations of a few miles.
       Air is readily separated into its components by fractional
distillation of liquid air. If it were a compound, it would all distil over
in a single fraction at a definite temperature.
       One of the first, who discovered the existence of the atmosphere
was notable Italian physicist Torricelli. To prove that there is such a
thing as a vacuum, he made an instrument consisting of glass tubing
890 mm long, sealed at one end and filled with mercury. Having
been inverted in a vessel containing mercury, the tube emptied partly.
Then he filled the remaining part of the vessel with coloured water
and raised the tube until its outlet was seen to reach the water. The
mercury suddenly dropped down from the tube and the water rushed
to the very top. The result made it plain that the space in the tube
above the mercury was empty. In such a way the existence of atmosphere
was proved.



                                    15