284 FETTERSSON, ON W AT Eli AND I C E. 



observations already collected long ago to corroborate this 

 fact. It bas long been a subject of discussion, whether the 

 ice is a brittle or a plastic substance. All observers agree, 

 that pnre ice, taken far below zero under ordinary pressure^ 

 is not plastic at all. Biit we nevertheless rnust confess, that 

 ice in the vicinity of 0° somehow or other can behave like a 

 plastic body, in order to account for a great many well known 

 facts ancl in the first place for the movement of the glaciers. 

 We may f. ex. attribute the fact, that two blocks of ice, which 

 are brought into contact in a warm room, immediately adhere 

 to each other like Avax, to the peculiar molecular state of the 

 ice par.ticles at the free surfaces, which by their contact are- 

 brought into altered conditions of cohesion, or we may ascribe 

 this and similar phenomena to a regelation, i. e. a temporary 

 melting process, caused by the lowering of the nielting point 

 by pressure and restoration of the initial state of aggregation, 

 as soon as the pressure ceases; we may, in short, declare the 

 plastic condition of the ice at its melting point to depend oii 

 an apparent instead of a real toughness of its substance — 

 but we still can not deny such observations, which plainly 

 show US, that every kind of ice, which we may test, softens. 

 before melting. 



In his admirable researches on tbe latent heat of melting^ 

 bodies, Person ^ observed some irregularities in the specific 

 heat of ice below zero, which led him to adopt the theory,. 

 that the ice does not melt at once at a fixed temperature, but 

 already some degrees below the melting point begins to weaken. 



The mechanical softening of pure ice below zero has been 

 testified by many observers. It Avill suffice to cite a few lines 

 from a paper by Pfaff entitled »Versuche iiber die Plasticität 

 des Eises». - 



»Es geht aus meinen Versuchen hervor, dass auch der 

 geringste Druck hinreicht, um Eistheilchen zu verschieben, 

 wenn er anlialtend icirJä und die Temperatur des Eises iind der 

 Umgebung nahe dem SchmehpnnMe ist.y 



»Es ergiebt sich, dass das Eis sich nahe seinem Schmelz- 

 punkte in der That wie Wachs verbalt und bei einem Druck& 

 von nur zwei Atmosphären sich so nachgiebig zeigt, dass z. B. 

 ein hohler Cylinder von Eisen von 11. 5 m.m. Durchmesser und 

 1.7 Wandstärke in zwei Stunden bei einer Temperatur zwischen 

 — 1 und 0.5 Grad 3 m.m. tief in das Eis eindrang. Welchen 



' C. R. XXX p. 526. 



2 Pogg. Ann. CLTV 1875. 



