[cooKE] VARIATION IN THE DENSITY OF ICE 129 
vessel; and so the next layer of ice is also formed on a surface which 
will expand on reaching a uniform temperature of zero. And the 
same reasoning will apply to the formation of each layer, till the 
process of freezing is completed. So, when the apparatus is finally 
transferred to a bath of ice and water, the outer layers of the forma- 
tion, including the walls of the vessel, will tend to expand, while the 
inner layers, being very near the freezing point, will tend to retain 
their dimensions. The effect of these stresses will be an increase in 
volume, and a corresponding decrease in density. 
In the case of the second formation where the water freezes 
around the outside of the vessel, the same reasoning will apply, the 
ice always forming on a surface which will tend to assume larger 
dimensions when its temperature is brought to zero. However, in 
this case, the contracted support for the newly forming ice is on the 
inside (see fig. 2), and so when the ice mantle is complete and the 

instrument placed in a zero bath, it is the interior layers, including 
the walls of the vessel, which tend to expand, this expansion being 
resisted by the exterior layers. These forces cause a certain amount 
of compression of the volume, and so the density assumes a higher 
value. 

Fie. 3: 
In the case of the column formation, represented diagrammatically 
in fig. 3, the explanation is somewhat more complex, as the difference 
