ON THE LAND. 217 



In our own islands, every one must have witnessed the 

 effects of frost on the rocks and soils. The water held in 

 the pores of all rocky substances is rapidly converted into 

 ice; in this state it expands, pushes asunder the par- 

 ticles, and when thaw comes, the separated particles, having 

 lost their cohesion, necessarily fall asunder, and are ready 

 to "be carried away by winds, rains, and runnels of water. 

 The force with which water expands in freezing is tremen- 

 dous. The strongest vessels are burst asunder ; the hardest 

 rocks are split into chips and fragments. Every winter we 

 see its effects in the disintegration of our ploughed soils, 

 and in the mounds of debris at the foot of our cliffs and 

 precipices. But under our insular climate the effects are 

 trilling compared with what takes place in higher latitudes 

 and in more elevated regions. In the higher Himalayas Dr 

 Hooker found the cliffs and precipices rent and rugged with 

 its force, and the ravines choked with the ruptured blocks 

 and fragments ; in Norway every peasant can point to the 

 mounds of angular blocks as the work of the " Bergrap ; " 

 and in Spitsbergen the Spanish Expedition found the 

 sea-cliffs fresh with recent rupture every winter severing 

 with its icy wedge, and every summer dissolving the connec- 

 tion. It is needless, however, to multiply instances ; every 

 intelligent mind must perceive the power of this recurring 

 ice-force, and its universality, in all the colder and higher 

 regions of the globe. And he has only to allow sufficient 



fanners. Even in the deserts of Africa, Arabia, and Persia, European 

 travellers have felt their effects. In Bengal, where ice is never formed 

 naturally, advantage is taken of the principle for its artificial pro- 

 duction. Shallow pits are dug, which are partially filled with straw, 

 and on the straw flat pans, containing water which has been boiled, are 

 exposed to the clear, dry, and serene firmament. The water is a power- 

 ful radiant, and sends off its heat rapidly into space. The heat thus 

 lost cannot be supplied from the earth, this source being cut off by the 

 non-conducting straw ; and before sunrise a cake of ice is formed in each 

 vessel 



