say, if you could measure off all the ground over which the rain fell, and spread the whole nine months’ rain over it, it would make a lake 500 inches, or more than 40 feet deep!  You will not be surprised that the country on the other side of these hills gets hardly any rain, for all the water has been taken out of the air before it comes there.  Again for example in England, the wind comes to Cumberland and Westmorland over the Atlantic, full of vapour, and as it strikes against the Pennine Hills it shakes off its watery load; so that the lake district is the most rainy in England, with the exception perhaps of Wales, where the high mountains have the same effect.

In this way, from different causes, the water of which the sun has robbed our rivers and seas, comes back to us, after it has travelled to various parts of the world, floating on the bosom of the air.  But it does not always fall straight back into the rivers and seas again, a large part of it falls on the land, and has to trickle down slopes and into the earth, in order to get back to its natural home, and it is often caught on its way before it can reach the great waters.

Go to any piece of ground which is left wild and untouched you will find it covered with grass weeds, and other plants; if you dig up a small plot you will find innumerable tiny roots creeping through the ground in every direction.  Each of these roots has a sponge-like mouth by which the plant takes up water.  Now, imagine rain-drops falling on this plot of ground and sinking into the earth.  On every side they will find rootlets thirsting to drink them in, and they will be sucked up as if by tiny sponges, and drawn into the plants, and up the stems to the leaves.  Here, as we shall see in Lecture VII., they are worked up into food for the plant, and only if the leaf has more water than it needs, some drops may escape at the tiny openings under the leaf, and be drawn up 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 shaken 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