254 
On Water and Air. 
[April, 
{erred, and which depends, as 1 have said, upon this polar 
force exerted by the molecules of matter. We will let the 
crystalHsation go on until it overspreads the entire screen 
The crystallisation of water upon the window pane on a 
frosty morning is quite as beautiful-perhaps m0I I e b ^ autlfu 1 
-than this. This effedt is exceedingly good. Mr. CoUrell 
has given himself great trouble to become master of this. 1 
have rarely seen it better than the exhibition that you have 
now before you. It is wonderful to see how the crystallisa- 
tion flashes forth, as it were, by sudden bursts of P ow ^> an 
falls into these beautiful shapes. I will content myself with 
one more sample of this architectural power exerted by the 
ultimate particles of matter. Here is a small cell which 
contains a solution. In our last ledture you saw that by 
means of our voltaic battery we decomposed water into xt 
two constituent parts, and converted the water into oxygen 
and hydrogen. I might have collefted the separate gases 
before you in your presence, and shown you that these gase 
were oxygen and hydrogen. In the same way we shall try 
to decompose this solution of acetate of lead , and here, 
instead of the plates of platinum which I employed last time, 
we have these little rods of platinum wire. They are ve ? 
clearly shown on the screen. We will now send a voltaic 
current across this solution in which these two wires are 
immersed, and you will find that on one of them the lead 
will be liberated ; but, instead of forming a kind of sand 
heap — a confused mass of the atoms of lead— those atoms 
of lead, as they are liberated, will build themselves up into 
most beautiful crystalline ferns. , ,. . , 
Mr. Cottrell has now sent the current through the liquid, 
and he has done so with caution, in order that you may ^see 
the growth of those little ferns of lead sprouting from that 
wire. You have a beautiful growth of lead crystals, thus 
showing, as I have said, the wonderful architectural power 
possessed by the atoms of lead when they are liberated. 
Nothing can be more beautiful than that slow growth. 
These beautiful fern-like masses resemble a formof vegeta- 
tion growing in your presence. I will now ask Mr. Cottrel 
to reverse the direftion of the eledtric current, and you will 
find these masses disappear, and, on the other side, you 
will find that the lead will be thrown out first of all in films 
like a spider’s legs. The crystals first formed will melt 
away, and the ferns will be produced on the opposite pole ot 
thebattery. [The current was reversed, and the crystalsot lead 
disappeared from one pole and were formed on the other.] 
This force of crystallisation which we have here mam- 
