54 THE FAIRY-LAND OF SCIENCE. 
on the banks of the Thames, and there was one ques- 
tion which often puzzled me greatly, as I watched the 
minnows and gudgeon gliding along through the 
water. Why should fishes live in something and be 
often buffeted about by waves and currents, while I 
and others lived on the top of the earth and not in 
anything? I do not remember ever asking any one 
about this ; and if I had, in those days people did not 
pay much attention to children's questions, and prob- 
ably nobody would have told me, what I now tell 
you, that we do live in something quite as real and 
often quite as rough and stormy as the water in which 
the fishes swim. The something in which we live is 
air, and the reason that we do not perceive it is, 
that we are in it, and that it is a gas, and invisible to 
us ; while we are above the water in which the fishes 
live, and it is a liquid which our eyes can perceive. 
But let us suppose for a moment that a being, 
whose eyes were so made that he could see gases as we 
see liquids, were looking down from a distance upon 
our earth. He would see an ocean of air, or aerial 
ocean, all round the globe, with birds floating about in 
it, and people walking along the bottom, just as we see 
fish gliding along the bottom of a river. It is true, he 
would never see even the birds come near to the sur- 
face, for the highest-flying bird, the condor, never 
soars more than five miles from the ground, and our 
atmosphere, as we shall see, is at least 100 miles high. 
So he would call us all deep-air creatures, just as we 
talk of the deep-sea animals; and if we can imagine 
that he fished in this air-ocean, and could pull one of 
us out of it into space, he would find that we should 
