It is while these bodies are burning that they look to us like
falling stars, and when we see them we know that hey must be
dashing against our atmosphere. Now if two people stand a
certain known distance, say fifty miles, apart on the earth and
observe these meteors and the direction in which they each see
them fall, they can calculate (by means of the angle between the
two directions) how high they are above them when they first see
them, and at that moment they must have struck against the
atmosphere, and even travelled some way through it, to become
white-hot. In this way we have learnt that meteors burst into
light at least 100 miles above the surface of the earth, and so
the atmosphere must be more than 100 miles high.
Our next question is as to the weight of our aerial ocean. You
will easily understand that all this air weighing down upon the
earth must be very heavy, even though it grows lighter as it
ascends. The atmosphere does, in fact, weigh down upon land at
the level of the sea as much as if a 15-pound weight were put
upon every square inch of land.
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