60 NOTE ON REGELATION. 
It will be understood that, in observing the flexible and rigid state 
of union, covvex surfaces of contact are necessary, so that the contact 
may be only at one point. If there be several places of contact, 
apparent rigidity is given to the united mass, though each of the 
places of contact might be in a flexible and, so to say, adhesive con- 
dition. It is not at all difficult to arrange a convex surface so that, 
bearing at two places only on the sides of a depression, it should 
form a flexible joint in one direction, and a rigid attachment in a 
direction transverse to the former. 
It might seem at first sight as if the flexible adhesion of the ice 
gave us a point to start from in the further investigation of the prin- 
ciple of pressure. If the application of pressure causes ice to freeze 
together, the application of tension might be expected to produce the 
contrary effect, and so cause liquidity and separation at the flexible 
joimt. This, however does not necessarily follow ; nor do I intend to 
consider what might be supposed to take place whilst theoretically 
contemplating that case. I think the changes of temperature and 
pressure are too infinitesimal to go for anything; and in illustration 
of this, will describe the following experiment. Wool is known to 
adhere to ice in the manner, as I believe, of regelation. Some wool- 
len thread was boiled in distilled water, so as thoroughly to wet it. 
Some clean ice was broken up small and mixed with water, so as to 
produce a soft mass, and, being put into a glass jar clothed in flan- 
nel that it might keep for some hours, had a linear depression made 
in the surface, so as to form a little ice-ditch filled with water ; in this 
depression some filaments of the wetted wool were placed, which, 
sinking to the bottom, rested on the ice only with the weight which 
they would have being immersed in water ; yet in the course of two 
hours these filaments were frozen to the ice. In another case, a 
small loose ball of the same boiled wool, about half an inch in 
diameter, was put on to a clean piece of ice; that into a glass basin ; 
and the whole wrapped up in flannel and left for twelve hours. At 
the end of that time it was found that thawing had been going on, 
and that the wool had melted a hole in the ice, by the heat conducted 
through it to the ice from the air. The hole was filled with the 
water and wool, but at the bottom some fibres of the wool were frozen 
to the ice. 
Is this remarkable property peculiar to water, or is it general to 
all bodies? In respect of water it certainly seems to offer us a glimpse 
