472 FROST-CLEFTS. 



fifteen degrees Reaumer (one and one-half degrees 

 Fahrenheit). Remeaux has shown that the temper- 

 ature of the concentric layers of wood by night in- 

 creases from outside to inside. A very severe, sudden 

 frost, that cools down the outer layers, must occasion 

 an important difference in temperature between 

 these and the inner, and at the same time a consid- 

 erable difference in relative bulk. The inner layers, 

 whether frozen or not, must considerably exceed 

 the outer, and thus increase the strain upon them," 

 and eventually causes the cleft. 



Sir James Eoss, in the history of his antarctic 

 voyage (Vol. I. p. 223), says : " We have often, in 

 arctic regions, witnessed the astonishing effect of a 

 sudden change of temperature during the winter 

 season, causing great fissures in the ice of many 

 miles in extent. A fall of thirty or forty degrees 

 in the thermometer immediately occasions large 

 cracks in every direction, attended with loud ex- 

 plosions. Some of them open several inches by 

 the contraction of the upper surface in contact with 

 the extreme cold of the atmosphere." Dr. Kane's 

 observations are similar, in his explorations of the 

 arctic regions. 



7. Wind Shakes — Anemosis : Berkeley. Aside 

 from the injury done by winds in breaking down 

 the limbs of trees, is that to the young and soft 

 shoots. By whipping these one against another, 



