150 Royal Society :—- 
takes place when there is no external force like pressure tending to 
bring the particles of ice together, but, on the contrary, a force of 
torsion is tending to separate them ; and, if respect be had to the 
mere point of contact on the two rounded surfaces where the flexible 
adhesion is exercised, the force which tends to separate them may 
be esteemed very great. The act of regelation cannot be considered 
as complete until the junction has become rigid; and therefore I 
think that the necessity of pressure for it is altogether excluded. 
No external pressure can remain (under the circumstances) after the 
first rigid contact is broken. All the forces which remain tend to 
separate the pieces of ice; yet the first flexible adhesions and all the 
successive rigid adhesions which are made to occur, are as much effects 
of regelation as those which occur under the greatest pressure. 
’ The phenomenon of flexible adhesion under tension looks ver 
much like sticking and tenacity ; and I think it probable that Pro- 
fessor Forbes will see in it evidence of the truth of his view. I 
cannot, however, consider the fact as bearing such an interpretation ; 
because I think it impossible to keep a mixture of snow and water 
for hours and days together without the temperature of the mixed 
mass becoming uniform; which uniformity would be fatal to the 
explanation. My idea of the flexible and rigid adhesion is this :— 
Two convex surfaces of ice come together; the particles of water 
nearest to the place of contact, and therefore within the efficient sphere 
of action of those particles of ice which are on both sides of them, 
solidify ; if the condition of things be left for a moment, that the 
heat evolved by the solidification may be conducted away and dis- 
persed, more particles will solidify, and ultimately enough to form 
a fixed and rigid junction, which will remain until a force sufficiently 
great to break through it is applied. But if the direction of the 
force resorted to can be relieved by any hinge-like motion at the 
point of contact, then I think that the union is broken up among the 
particles on the opening side of the angle, whilst the particles on the. 
closing side come within the effectual regelation distance ; regelation 
ensues there and the adhesion is maintained, though in an apparently 
flexible state. The flexibility appears to me to be due to a series of 
ruptures on one side of the centre of contact, and of adhesion on the 
other,—the regelation, which is dependent on the vicinity of the ice 
surfaces, being transferred as the place of efficient vicinity is changed. 
That the substance we are considering is as brittle as ice, does not 
make any difficulty to me in respect of the flexible adhesion ; for if 
we suppose that the point of contact exists only at one particle, still 
the angular motion at that point must bring a second particle into 
contact (to suffer regelation) before separation could occur at the 
first ; or if, as seems proved by the supervention of the rigid adhesion 
upon the flexible state, many particles are concerned at once, it is not 
possible that all these should be broken through by a force applied 
on one side of the place of adhesion, before particles on the opposite 
side should have the opportunity of regelation, and so of continuing 
the adhesion. | 
It is not necessary for the observation of these phenomena that a 
earefully-arranged water-vessel should be employed. The difference 
