On Water and Air . 
[May, 
328 
intents and purposes, icebergs. The glaciers of Greenland 
work their way down into the real ocean, and the ends of 
these glaciers breaking away in large masses are sent float- 
ing out to sea ; and it is these icebergs which constitute 
some of the dangers of the Northern Atlantic. It was one 
of these with which a vessel came into collision some time 
ago. That iceberg against which the vessel impinged came 
from one of these northern glaciers. It was a bit of one of 
these northern glaciers, broken off and sent into the ocean 
like the small masses of ice from the Swiss glaciers carried 
into the Margelin See. 
Now I must give a wrench to this topic, and pass on to 
another subject. . 
We have to consider this atmosphere, and the physical 
properties of the air which, in the long run, has sustained 
the weight of all our glaciers and of all our rivers. It is a 
constantly observed fa ft that when there is a great advance 
in science there is always a general simmering and fermen- 
tation of scientific thought for some time previously, and 
by-and-bye some particular individuals rise, so to say, out 
of this general fermentation, and initiate the real principle 
or law, or whatever it may be, about which people are 
thinking during this intelleftual simmering. And so it was 
some three hundred years ago with regard to our atmo- 
sphere. People did not know that the atmosphere had 
weight. It was shrewdly suspefted, however, by that 
great man, Galileo, and by Descartes, that the atmosphere 
had weight. But this was not clearly made out even in 
their day, and when we consider the knowledge that is now 
open to every little boy and girl it is strange that this 
knowledge was held back from those truly great men of 
antiquity, men of the very greatest intellects. We have 
now to deal with results which they would have, given 
anything to know, and which are now perfectly familiar to 
us. Descartes realised that the air has weight. The weight 
of the air in this room in which you are now assembled — 
what would you guess it to amount to ? Perhaps you 
would say that it weighed a few pounds ; but the weight 
of 13 cubic feet of air is about a pound. There are per- 
haps nearly 80,000 cubic feet of air in this room ; and if 
vou make a calculation you will find that the air in this 
room at the present time would weigh something about 
three tons. That, perhaps, you would not expeft. Now 
we have the air here with the whole of the atmosphere 
above us. Some make the atmosphere of one height, some 
of another. There are various reasons why we should give 
