50 
On Water and Air . 
[January, 
would be reduced in weight to 15 pounds, so that, out of 
the 64 pounds, nearly 50 pounds are pure water. Hence I 
think you will agree with me that I am not wrong in stating 
that water is a very important article of food. Every mutton 
chop and every beefsteak that we consume contains water 
in this proportion. 
But we not only thus feed upon water, but we drink it 
diredtty. Whence comes our drinking water ? Well, any 
thoughtful boy or girl here present who had time to think 
would say that, eventually, it comes from the clouds. How 
does it get there ? That question can be answered tho- 
roughly by-and-bye. At the present time we know, or at 
all events we assume, that the water comes first of all 
from the clouds. If you trace the course of the Thames 
backwards, you find that the very broad river that we have 
here in London is joined by other rivers right and left, 
until, finally, you come to the Cotswold Hills, where you 
find that what is here the Thames comes down to a small 
rivulet. This rivulet is joined by other rivulets on the 
right and left as you go down it, and then, at last, the river 
assumes the breadth at which we have it here when it 
reaches London. Now, this water which comes from the 
Cotswold Hills falls on those hills as rain. But not only 
does the water flow thus over the surface of the collecting 
valleys, and then flow to the sea in tke form of rivers, but 
it in part sinksinto the ground and percolates through the soil, 
and here and there appears as a pellucid spring. That is 
the origin of spring-water. It comes originally from the 
clouds, but it has percolated through the earth and come 
out somewhere, and there we have our clear spring. 
Now, the hardest rocks are more or less soluble in water. 
You know that sugar and salt are very soluble ; but rocks 
are also more or less soluble in water, so that all our river- 
water and spring-water has more or less of mineral matter 
dissolved in it, as sugar is dissolved in a cup of tea. Well, 
how do we know this ? A great portion of the mineral 
matter may be removed from the water merely by boiling, 
and it is so removed in all our utensils which are employed 
in the kitchen. Just before the lecTure I went into our own 
kitchen upstairs, and I looked into this kettle, and I found 
a thick mineral incrustation. I dare say that I can get this 
very hard substance out of the interior, and if you look at 
the interior surface of that kettle after the ledture, you will 
see that it is covered by this very thick crust, which is so 
very hard that I can hardly get it to break away. Here it 
is. There is a crust of this thickness on the interior surface 
