48 THE BOOK OF NATURE STUDY 



come gradually into regions where the water becomes warmer 

 and warmer. Let us take a dish of warm water and put one 

 of our miniature icebergs into it, choosing one of irregular shape, 

 to imitate as far as possible a natural form. If the experiment 

 is carried out in a glass vessel we shall see the base of the ice- 

 berg gradually diminish, as its substance is as it were eaten away 

 by the action of the warm water. Sooner or later probably 

 the little berg will topple over as it becomes too heavy for its 

 base. When this has been noticed in the mimic berg, descrip- 

 tions may be given of the crashing of the real bergs as their lower 

 submerged portions melt, and they reel over with a tremendous 

 splash. 



Again, we notice as the ice melts how it chills the water, 

 chills also the air, and how, if there be much ice in proportion 

 to the water, there probably forms on the outer side of the glass 

 a misty vapour. One would then repeat what has been already 

 said as to the effect of cooling the air, and at the same time speak 

 of the dense mists which occur in the vicinity of icebergs, or where 

 a current of water cooled by melting ice reaches a region where 

 the air is comparatively warm. We may also read a passage from 

 Rudyard Kipling's Captains Courageous to emphasise the danger 

 to navigation which results. In this way one would pass to 

 explanations of fog and mist, showing by examples that as the 

 air above water is always full of water vapour, any chilling down 

 of it tends to produce fog or mist. The mist which forms in river 

 valleys on calm evenings helps to illustrate the same fact. 



Again, if ice floats in water it is because it is lighter than 

 water. The question at once arises how much lighter ? Let 

 us put into our measuring-glass a certain amount of warm water, 

 and drop into it a piece of ice. The teacher should find by ex- 

 periment beforehand the necessary size to cause the water to 

 rise to a convenient height. The ice of course floats, but nine- 

 tenths of its bulk is submerged, and this causes the water in the 

 glass to rise through a certain distance. We allow the ice to 

 melt, and find that the water stands at the same level as it did 

 when the ice was floating in it. An attempt should be made 

 to show that this means that when ice melts the resultant water 

 represents only about nine-tenths of the bulk of the ice, or in 



