it was generally supposed not to be more than fifty miles. But
lately, some curious bodies, which we should have never suspected
would be useful to us in this way, have let us into the secret of
the height of the atmosphere. These bodies are the meteors, or
falling stars.

Most people, at one time or another, have seen what looks like a
star shoot right across the sky, and disappear. On a clear
starlight night you may often see one or more of these bright
lights flash through the air; for one falls on an average in
every twenty minutes, and on the nights of August 9th and
November 13th there are numbers in one part of the sky. These
bodies are not really stars; they are simply stones or lumps of
metal flying through the air, and taking fire by clashing against
the atoms of oxygen in it. There are great numbers of these
masses moving round and round the sun, and when our earth comes
across their path, as it does especially in August and November,
they dash with such tremendous force through the atmosphere that
they grow white-hot, and give out light, and then disappear,
melted into vapour. Every now and then one falls to the earth
before it is all melted away, and thus we learn that these stones
contain tin, iron, sulphur, phosphorus, and other substances.

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