82 THE FAIRY-LAND OF SCIENCE. 
the tiny openings under the leaf, and be drawn np 
again by 'the sun-waves as invisible vapour into the 
air. 
Again, much of the rain falls on hard rock and 
stone, where it cannot sink in, and then it lies in pools 
till it is shake apart again into vapour and carried 
off in the air. Nor is it idle here, even before it is 
carried up to make clouds. We have to thank this 
invisible vapour in the air for protecting us from the 
burning heat of the sun by day and intolerable frost 
by night. 
Let us for a moment imagine that we can see all 
that we know exists between us and the sun. First, 
we have the fine ether across which the sunbeams 
travel, beating down upon our earth with immense 
force, so that in the sandy desert they are like a 
burning fire. Then we have the coarser atmosphere of 
oxygen and nitrogen atoms hanging in this ether, and 
bending the minute sun-waves out of their direct path. 
But they do very little to hinder them on their way, 
and this is why in very dry countries the sun's heat is 
so intense. The rays beat down mercilessly, and 
nothing opposes them. Lastly, in damp countries we 
have the larger but still invisible particles of vapour 
hanging about among the air-atoms. Now, these 
watery particles, although they are very few (only 
about one twenty-fifth part of the whole atmosphere), 
do hinder the sun-waves. For they are very greedy 
of heat, and though the light-waves pass easily through 
them, they catch the heat-waves and use them to help 
themselves to expand. And so, when there is invisible 
vapour in the air, the sunbeams come to us deprived 
