ON THE CONTRACTION AND EXPANSION OF ICE. 423 
the temperature not remain stationary, but change within the four 
hours, the action and movement of the ice would be accordingly 
checked and modified. 
The lagging behind of the ice, and consequently its not responding 
readily to rapid changes of temperature, is well illustrated on the 
diagram by observations Nos. 55, 62, 65, 73, 84, 92, 96, 100, 120, 
and 158. . 
The atmosperic temperature, during the period of my experiment, 
did not fall below minus 4°. I found, however, in a range of 38°, that 
is, from minus 4° to plus 34°, the contraction and expansion at any 
degree within this range was uniform. 
I think, therefore, that we may fairly assume that it preserves that 
uniformity to the lowest temperature known im this country. 
In addition, therefore, to the deductions made in a former paper, 
may we not glean and add the following :— 
That with the same change of temperature, the expansion and con- 
traction of ice are equal. 
That the fact that ice on a large field exceeds, during subsequent 
expansion, the limits of its first dimensions, is owing to the peculiar 
manner of its previous contraction. . 
That the rapidity of ice movement, due to change of temperature, 
is inversely as its thickness. 
That the rate of expansion and contraction of pure ice (as mea- 
sured by a deal rod, for which no allowance was made), is .00000 330 
of its length per degree; and that of ordinary ice .00000 765. 
Having brought to a conclusion these very interesting experiments, 
the object of which was to sustain and fully confirm the theories and 
conclusions previously deduced from a much larger field of observa- 
tion, which it has done, with one exception, not only as regards the 
general theory but also with respect to the expansive capacity of ice, 
I now leave the subject with the hope that these preliminary inves- 
tigations, on a body whose properties seem so little known to the 
scientific world, may yet throw important light on the perplexing 
glacier phenomena, and also with the hope that at other hands it may 
receive a further and more thorough investigation. 
