On Water and Air. 
25B 
[April, 
of the quantity melted. I had a letter from Switzerland 
yesterday morning, and at the present time the quantity of 
snow upon the mountains at Brieg, in the valley of the 
Rhone, is comparatively small, although the cold is very 
great. That is an important point to notice. In point of 
fadt, there is not sufficient aqueous vapour in the air to 
produce snow, however cold the weather may be. 
And here let me draw attention, in passing, to a point 
which has misled many not only eminent, but very illustrious, 
men. If you go to Switzerland, or even to some parts of 
England, you find traces of ancient glaciers. If you go to 
Cumberland, or to Wales, or to the south-west coast of 
Ireland, you find traces of ancient glacier adtion which are 
just as pronounced and clear as the traces of glacier adtion 
that are going on to-day in Switzerland. In trying to 
account for the period in which glaciers extended over nearly 
the whole of Europe some eminent men have put forth their 
suppositions. One celebrated notion is that the radiation of 
the sun, by some means or other, was diminished — that the 
solar power became diminished, and that, in consequence of 
the chill, we had the Glacier Epoch. There is also another 
supposition : it is more than a supposition. It has been 
thought that the whole of our solar system is moving through 
space ; and it was supposed that, in passing through space, 
the solar system has passed through spaces which have a 
very low temperature, and that during its passage through 
those spaces of low temperature the Glacier Epoch, as it is 
called, was produced. Now I think that every boy in this 
assembly will see the defedt of this reasoning. At the pre- 
sent moment, as recorded to me yesterday by a letter from 
Switzerland, the cold is intense, but the quantity of snow 
which produces glaciers is very little. Why? You are pre- 
pared with your answer. The very material of which gla- 
ciers are formed is absent. The air is dry, notwithstanding 
the great cold, and the consequence is that you have very 
little precipitation of snow, and very little of that nutriment, 
or of that material, which produces glaciers. I want you to 
understand that these vast masses of ice which come down 
the Alpine valleys are entirely due to the congelation of 
aqueous vapour and its precipitation as snow ; so that it is 
the aqueous vapour which produces the snow. I hope you 
will see my reasoning. The very agency which gives birth 
to these large masses of ice which form the glaciers is heat. 
You could not have those vast masses of ice without having 
vapour raised from the tropical ocean. This vapour is 
carried northward ; it is congealed in the atmosphere, and 
