GLACIEES AND ICE. 
53 
tion (see Plate IV.).* It is the intangible fairy lieat that has 
worked this spell. The ice was laid down according to the same 
laws that shape the snow into those beautiful and well-known 
crystalline forms so often to be seen in snow-storms here and 
elsewhere. Ice is indeed only an aggregate of crystals similar 
to those of snow ; which lying together in perfect contact, as 
we have already explained, render each other invisible and 
the block transparent. When the heat of the gas-flame 
entered the slab, it set to work to pick the ice to pieces, by 
giving it, in certain places, a rapid molecular shaking, and 
the fairy-flowers which appear in the warmed ice are the result 
of this agitation. On a priori grounds, we should therefore 
infer that the shape of these liquid crystals — for they are 
merely water — would be the same as the solid crystals which 
originally built up the ice. This is found to be the case. In 
order to make the comparison easy, I have shown, side 
by side, in the upper part of the plate some snow crystals 
taken from Mr. GlaishePs drawings, and a few of the most 
characteristic shapes of the “ ice-flowers.” The two are 
seen to be identical ; each have six rays, and the serrations in 
both follow the common angle of 60°. Just as the ice freezes, 
so, under suitable conditions, it liquefies ; the ice-flowers, or 
negative crystals, appearing in the same plane as that in which 
they were formed. The air-bubbles in ice show this direction. 
The bubbles collect in widely distant layers, marking the 
successive stages of freezing; between the layers there is 
either a clear intervening space or those perpendicular rows of 
bubbles already noticed. Accordingly the ice freezes parallel 
with the former, and at right angles with the direction of the 
latter bubbles. Some of both classes of bubbles are shown 
in the plate, their position relative to the ice-flowers being 
thus indicated. 
In the plate the artist has striven to show, as faithfully as 
possible, the result of the internal liquefaction of a block of 
ice through the agency of heat from a luminous source. 
For the rays from a fire, the sun, or the electric light, are 
equally competent to develop the flowers ; but they can- 
not be so well produced by a lamp, when the flame is 
surrounded by glass chimneys, f Beautiful as the plate 
appears, it is, however, impossible for the most skilful artist 
* It is to Dr. Tyndall we are indebted for this revelation of the structure 
of ice. 
f I have to thank Mr. W. West for the care with which he repeatedly 
examined blocks of ice whilst making the engraving from the substance itself. 
In order to give a general idea of the disintegration the artist has combined 
two or three points of view : this will account for anything appearing like 
irregularity, where, naturally, all is order and precision. 
