CLOUDS AND RIVERS, ICE AND GLACIERS. 119 



properties of water that ought to be familiar to enquirers 

 like you and me. 



302. In our dissection of lake ice by a beam of heat 

 ;§ 11) we noticed little vacuous spots at the centres of 

 the liquid flowers formed by the beam. These spots we 

 referred 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 subject. 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 heat ; 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 warmed thermometer. 



306. 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 



