52 
POPULAR SCIENCE REVIEW. 
v/hich might be compared with that of soft wax. But ice is only plastic- 
under pressure ; it is not plastic under tension ; and this is the important- 
point which the vague theory of plasticity was unable to explain. 
It is tlien by fracture and regelation that glaciers are able 
to flow, and weld themselves together like streams of lava. 
But our readers are probably wondering whether other bodies 
besides ice possess this convenient natural cement. Appa- 
rently they do not, for as far as the experiments which Mr. 
Faraday has made on this point have gone, it seems a special 
property of ice.* Regelation only takes place when the two 
surfaces of ice are in a melting condition, but if in this state 
it invariably occurs. In water as well as in air, fragments of 
ice will instantly freeze together by the gentlest contact ; and 
even under water as hot as the hand can bear, two pieces of 
rapidly melting ice may suddenly be frozen into one by merely 
bringing them together. The cause of the phenomenon of 
regelation has been the subject of much controversy among 
scientific men. It would take us too far from our subject to 
enter into it here, but it may be stated that the original 
explanation given by its discoverer, whilst being of the 
highest interest, harmonizes with all the facts, f 
Ice is one of those bodies which nature appears to have put 
together with special care ; for, it may be only subjectively, 
there are some natural objects which after a prolonged 
examination seem more wonderful than others. Let us look 
at the substance itself. Here is a block of clear ice, such as 
any fishmonger can supply. Rows of air-bubbles can be seen 
running parallel to each other throughout the mass ; and in 
some irregular places there is a fine gauze-like appearance 
produced by a web of minute bubbles. This is but the poetical 
way in which ice expresses a split; for this beautiful, netting 
is the result of nothing more than some accidental blow. 
Gutting a slice from the block across the bubbles, let us hold 
it close to a naked gas-flame (the reason for which will be 
seen directly), and now let us observe it. The lamp of 
Aladdin could not have wrought a more wondrous change. 
The part before clear and unmarked is now studded all over 
with lustrous stars, whose centre shines like burnished silver. 
A fairy seems to have breathed upon the ice and caused trans- 
parent flowers of exquisite beauty suddenly to blossom in my- 
riads within the ice, and all with a charming regularity of posi- 
* Proc. Royal Society, vol. x. p. 440. 
t Published as report of lecture by Mr. Faraday, in the Athenceum, 1850, 
p. 640 ; and “ Experimental Researches in Chemistry and Physics,” p. 377. 
See also a paper by Professor Tyndall, in the December number of the 
Philosophical Magazine , for a resurrd of the discussion. 
