256 
On Water and Air. 
[April, 
This mixture is chilled by the evaporation of the ether, and 
the chilled brine is carried round vessels containing water, 
and then the water is converted into the solid form by the 
chill produced by the cold brine. And now, not only are 
those beautiful crystalline forms that you see upon the 
London pavement, and upon your own windows on a frosty 
mornings evidences of this wonderful building power 
possessed by the ultimate particles of matter, but every 
partfcle of ice that spreads over the Serpentine or covers 
the lakes of Switzerland and Norway at the present moment, 
is built upon this wondrous plan ; and I want, if I can, tc 
dissedt in your presence a plate of ice. I see that • 
Cottrell has got a plate of ice there before you, and I will 
tell you how it was that this disseaion, or analysis, if you 
like to call it so, occurred. I remember walking thro g 
Kensington Gardens, I think, in the year 1858. Msmy 
you were not born then. And I thought to mysdf lce 
absorbs or stops a very considerable amount of heat. What 
becomes of that heat ? ” I knew that the ice, when once 
raised to the point when it begins to melt, could not be 
raised higher in temperature. 
You may remember that in our last ledVure I placed a p> 
of rock salt and a plate of glass in the path of our f ™ n f 
beam. The plate of rock salt was not warmed. The plate 
of glass was heated. And then we inferred from that fa<5t 
that a certain amount of heat was stopped by the glass, but 
was not stopped by the rock salt. I asked myself, in walk g 
through Kensington Gardens, “ What occurs m the melting 
of a block of ice when a sunbeam has g° ne through it . A 
good deal of the sunbeam is intercepted : W h at becomes o 
it ? It cannot warm the ice : then it must liquefy it in some 
peculiar way within the mass of ice. Well, I got a clear 
block of ice ; and I went into the room through which you 
passed in coming into this theatre, and the sun was shining 
brightly : and I placed a lens in the path of the sunbeams, 
and there I could see, as you have seen over and over again 
in this room, the track of the sunlight depicted u P on 
floating dust of the air. I fixed the point where the light 
was converged, and I put my block of ice so that the focus 
of the lens should be in the very heart of the ice. Immedi- 
ately I saw a number of little specks of silvery bngh ness in 
the very body of the ice. That did not at all solve the prr- 
blem I had in hand. I asked myself, “ What has become o 
the heat?” I took up the ice, and looked at it by means of 
a nocket-lens and I found that round about each one of 
these spots I had a most delicate and beautiful little liquid 
