IN CLOUDS AND RIVERS. ICE AND GLACIERS. 



Our tlrst effort to sound the moulin fails 

 through the breaking of our cord by the im- 

 petuous plunge of tho water. A lump of 

 grease in the hollow of a weight enables a 

 mariner to judge of a sea bottom. We em- 



C" ' such a weight, but cannot reach the 

 of the g'uc er. A depth of 163 feet is 

 the utmost rtajhed by our plummet. 



300. From July 28th to August 8th we have 

 watched the progress of the Grand Moulin. 

 On the former date the position of the mou- 

 lin was fixed. On the 31st it had moved 

 down 50 inches ; a little more than, a day 

 afterward it had moved 74 inches. On 

 August 8lh it had moved 198 inches, which 

 gives an average of about 18 inches in 

 twenty four hours. No doubt next summer 

 upon the Mer de Glace a Grand Moulin will 

 be found thundering near Trolaporte ; but 

 like the crevasse of Hie Grand Plateau, al- 

 ready referred to ( 1(5), it will not be our 

 moulin. This, or i at her the ice which it 

 penetrated, is now probably more than a 

 mile lower down than it was in 1857. 



45. THE CHANGES OF VOLUME OF WATER 



BY HEAT AND COLD. 



SOI. We have noticed upon the glacier 

 shafts and pits filled with water of the most 

 delicate blue. In some cases these have been 

 the shafts of extinct moulins closed at the 

 bottom. A. theory has been advanced to ac- 

 count for them, which, though it may be un- 

 tenable, opens out considerations regarding 

 '.he properties of water that ought to be 

 familiar to inquirers like you and me. 



302. In our dissection of lake ice by a 

 beam of heat ( 11) we noticed little vacu- 

 ous spots at the centres of the liquid flowers 

 formed by the beam. These spots we re- 

 ferred to the fact that when ice is melted the 

 water produced is less in volume than the 

 ice, and that hence the water of the flower 

 was not able to occupy the whole space 

 covered by the flower. 



303. Let us more fully illustrate this sub- 

 ject. Stop a small flask water-tight with a 

 cork, and through the cork introduce a 

 narrow glass tube also water-tight. It is 

 easy to fill the flask with water "so that the 

 liquid shall stand at a certain height in the 

 glass tube. 



304. Let us now warm the flask with the 

 flame of a spirit-lamp. On first applying the 

 flame you notice a momentary sinking of the 

 liquid in the glass tube. This is due to the 

 momentary expansion of the flask by ha.t ; 

 it becomes suddenly larger when the flame is 

 first applied. 



305. But the expansion of the water soon 

 overtakes that of the flask and surpasses it. 

 We immediately see the rise of the liquid 

 column in the glass tube, exactly as mercury 

 rises in the tube of a watmed thermometer. 



800. Our glass tube is ten inches long, and 

 at starting the water stood in it at a height of 

 five inches. We will apply the spirit-lamp 

 flame until the water rises quite to the top of 

 the tube and trickles over. This experiment 

 suffices to show the expansion of the wale? 



by heat. 



307. We now take a common finger-glass 

 and put into it a little pounded ice and "salt. 

 On this we place the flask, and ihen build 

 round it the freezing mixture. The liquid 

 column retreats dosvn, the tube, proving the 

 contraction of the liquid by cold. We allow 

 the shrinking to continue for some minutes, 

 noticing that the downward retreat of the 

 liquid becomes gradually slower, and that it 

 finally ceases altogether. 



308~. Keep your eye upon the liquid col- 

 umn ; it remains quiescent for a fi action of 

 a minute, and then moves once more. But 

 its motion is now upward instead of down- 

 ward. The freezing mixture now acts exactly 

 li/ce theflatne. 



309. It would not be difficult to pass a 

 thermometer through the cork inio the 

 flask, and it would tell us the exact tempera- 

 ture at which the liquid ceased to coii tract 

 and began to expand. At that mumtnt we 

 should find the temperatuic of the liquid a 

 shade over 39 Fahr. 



310. At this temperature, then, water at- 

 tains its maximum density. 



311. Seven degrees below this temperature, 

 or at 32 Fahr., the liquid begins to turn into 

 solid crystals of ice, which you know swims 

 upon water because it is bulkier for a given 

 weight. In fact, this halt of the apprracb- 

 ing molecules at the temperature of 39", is 

 but the preparation for the subsequent act of 

 crystallization, in which the expansion by 

 cold culminates. Up to the point of solidin> 

 cation the increase of volume is slow and 

 gradual ; while in the act of solidification it 

 is sudden, and of overwhelming strength. 



312. By this force of expansion the Floren- 

 tine Academicians long ago burst a sphere 

 of copper nearly three quaiters of an inch in 

 thickness. By the same force the celebrated 

 astronomer Huyghens burst in 1GG7 iron can- 

 nons a finger breadth thick. Such experi- 

 ments have been frequently made since. 

 Major Williams during a severe Quebec win- 

 ter filled a mortar with water, and closed it 



i by driving into its muzzle a plug of wood. 



i Exposed to a temperature 50 Fahr. below 

 the freezing point of water, the mKal resist- 

 ed the strain, but the plug gave wy.y, b( ing 

 projected to a distance of 400 feet. At 

 Warsaw howitzer shells bave been thus ex- 

 ploded ; and you and I have shivered thick 

 bomb-shells to fragments by placing them 

 for half an hour in a freezing m'xture. 



313. The theory of the shafts and pits re- 

 ferred to at the beginning of inis section is 

 this : The water at the surface of the shaft 

 is warmed by the sun, say to a temperature 

 of 39 Fahr. The water at the I ottom, in 

 contact with the ice, must be at 32 or near 

 it. The heavier water is therefore at the 

 top ; it will descend to the bottom, melt the 

 ice there, and thus deepen the shaft. 



314. The circulation here refeired to un- 

 doubtedly goes on, and some curious ejects 

 are due to it ; but not, I think, the one here 

 ascribed to it. The deepening of a shaft im- 

 plies a quicker melting of its bottom than of 



