40 
it, except at its surface. Blocks of ice may be seen in the windows of ice 
shops with the sun shining full upon them, and melting nowhere but on their 
surfaces. And the experiment of the ice-lens shews that heat may stream 
through ice in abundance — of which a portion is necessarily stopped in the 
passage — without melting it, except on its surface. My theory supposes 
that the ice beneath the surface of a glacier is a solid. That is all. 
Being a solid, and receiving into its substance heat — that is force — in 
great quantities, that force (by the principle of the conservation of 
force) cannot but be stored up in it, under the form of " potential energy," 
and wherever it is present, produce a tendency to dilatation. When that 
tendency takes effeet, it is in the direction of the least resistance to the 
dilatation ©f that part. It matters not whether the temperature of the ice 
be below 32° or above it, provided only that the condition of solidity be 
satisfied. Being a solid, it cannot but dilate and contract under the variations 
of temperature to which it is subjected; and dilating and contracting it 
cannot but descend. To shew that the ice of a glacier does not dilate 
when heat is received into it, it would be necessary to shew it not to be 
subject in this respect to a law common to all other bodies. 
Great alternations of temperature are not necessary to cause the motion 
of a glacier. A succession of small alternations produce the same effect as 
one great one. Their effect is cumulative. Alternations backwards and 
forwards, of 2 Q each, six times repeated, would carry the glacier (under 
certain assumed conditions) as far down as a single alternation of 12°. 
XI 
NoTfls on Rain- Water collected in Bristol. 
By W. W. Stoddart, F.G.S., F.C.S. 
Bead at the General Meeting, December Ind, 18C9. 
Those, who heard a paper by the author at a late meeting of the 
Microscopical Society, will recollect that some slides and drawings of the 
various salts &c. found in rain-water were exhibited. 
Since then Dr. Angus Smith has published engravings of the residues of 
rain-water collected iu the north of England, but the crystals differ so much 
