On Water and A ir * 
255 
1880.] 
fested and illustrated comes into play when water passes 
from the vaporous condition into the solid condition in our 
atmosphere ; and, not only so, but it comes into play in 
every mass of ice upon our lakes. There are before you 
some splendid masses of ice. This is not natural ice, but 
it is ice which has been artificially produced by the General 
Ice Factory Company, a company that has instituted itself 
for the production of this article, ice, in London. Now, I 
want to show you how it is that these masses of artificial 
ice are produced. I have never seen such a large block of 
artificial ice as this before. This ice is produced very 
cheaply — so cheaply as to compete successfully with the ice 
which is brought from the lakes of Norway. The cheapness, 
however, you and I care very little about as regards that 
about which I now wish to speak to you. Here is a clear 
liquid called sulphuric ether, and upon the face of this 
thermo-eleCtric pile I will place the copper basin, B (Fig. 28). 
Fig. 28. 
I will warm the basin a little so that the red end of the 
needle, connefted to the pile by the wires G, shall come well 
towards me ; and now I pour a little of this sulphuric ether 
into the copper basin, and I will warm the liquid by simply 
rubbing it round with my warm fingers. I want you to 
notice the effect of the evaporation of that ether. It is a 
very volatile substance, and, when it evaporates, the evapo- 
ration is accompanied by the chilling of the ether, so that, 
although, in the first instance, the needle will rest in its 
present position upon the side of heat, still, after a little 
time, in virtue of the evaporation of the ether, which evapo- 
ration will infallibly be associated with a chill, the needle 
will come down, and will pass to the other side. You will 
see that in this way, by the simple evaporation of the ether, 
we have produced a very great amount of cold. There, you 
see that we have got an amount of cold which has carried 
the needle from where it was down across zero, and far away 
in the direction of cold. Now, this artificial ice is produced 
exactly by such means. A mass of ether is caused to sur- 
round vessels in which is contained brine, or salt and water. 
