On Water and Air . 
251 
1880.] 
these cannot be compared in point of beauty with the snow 
crystals that fell upon my hat at that time. I say that this 
is a rude and crude form in comparison with the beauty ot 
the crystal itself. I wish you to remember that in all cases 
the crystalline form is preserved. You always have six ot 
those leaves, and no deviation from that number. You may 
have deviations in the form of the leaves, but there is no 
deviation whatever from the six-leaved form. Mr. Cottrell 
Fig. 26. 
will show you another, and you will find in every case this 
six-leaved stellar form of the snow. There is no deviation 
from this rule. ... 
Now I want to try to make clear to you how it is that 
scientific men explain to themselves this wondrous archi- 
tectural power, if I may so speak, displayed in the building 
up of these crystals. We have a number of these crystal- 
line bodies here. For instance, this block is a piece of rock 
crystal, and here we have a specimen of artificial crystal. 
Here is a crystal of sulphate of copper, and in the front 
here you have a mass of alum crystals ; and here, thanks to 
Messrs. Hopkin and Williams, I have a number of artificial 
crystals. Now I want you to be able to realise the mode in 
which scientific men represent to their minds how these 
wonderful crystals are built up. Here I have what every 
boy or girl is more or less acquainted with, a bar magnet; 
and here is a magnetic needle. If I hold this magnet thus 
