( 460 ) 
exactly the place of the immerged part, and accordingly leave the 
position of the surrounding water intact. 
In short: the ice when melting contracts into the volume of the 
immerged piece. 
§ 3. A more elaborate, but perhaps more graphical demonstration 
is the following. 
Let the piece of ice have the volume of A liter. Then the volume 
of the free part is 83 A cm. and of the immerged volume 917 
A cm. The immerged part gives, when melting, 841 A em. of water, 
the free piece 76 A cm. of water. The water of the free piece supplies 
therefore what the immerged piece had lost in volume when melting, 
and there is no reason for change in the level of the surrounding 
water. 
In this the specific gravity of ice is put at 0,917. 
§ 4. It is obvious, that the same reasoning applies to other sub- 
stances, so that the following general rule may be drawn up : when 
a substance, floating in its own melting-liquid, melts, the level of 
the liquid will not change. 
$ 5. An application of everyday interest is this: if a glass is 
filled to the brim with water, in which ice floats, the water will 
not flow over when the ice melts. 
We should, however, take care, when making the experiment with 
a full glass, not to mistake water that is condensed on the cold 
outside wall, and runs down, for water flowing over. A better proof 
is furnished by a glass which is not quite full of water, and on 
which the first level is indicated: after melting we must find the 
same level. 
§ 6. Attention may be called to the fact that not only after, but 
also during the melting the level is the same as before. 
For if one gramme of ice (or a given part of it) melts and gives 
one cm. (or an equally large part of it) of water, the weight of the 
floating piece and so also the upward pressure will be diminished 
by one gramme (or an equally large part of it), and consequently 
the volume of the immerged piece will be decreased by one em. (or 
an equally large part of it). For the additional water room has been 
made by the decrease in displacement. 
§ 7. The law of the permanent level holds also when the floating 
ice has empty cavities. 
