418 



ICE PHENOMENA. 



I have witnessed in several shoves that when the ice contracted, the 

 fractured and elevated pieces, which previously came in contact with 

 each other, would fall, and perhaps partly under the field ice. A 

 space in the centre thus presented open water. This open water 

 has probahly been mistaken for a fissure caused by contraction. 



I have he^rd of open fissures that have been seen eighteen inches 

 in width, and this I think under peculiar circumstances, quite proba- 

 ble. That these fissures do sometimes occur, and that they never do 

 occur unless the thermometer indicates a decided fall of temperature, 

 is sufficient proof that ice contracts by a change to a temperature 

 lower than that which had just previously existed. I may add, that 

 contraction occurs generally at night, and is accompanied by sharp 

 reports. A uniform temperature of the atmosphere does not cause 

 either expansion or contraction of ice ; it matters not whether the 

 temperature be high or low, no movement of any kind takes place. 

 A coating of snow of any depth over six inches eifectually prevents 

 any motion in ice, by protecting it from the influences' of the atmos- 

 phere. 



I find from repeated experiment that the upper stratum of ice par- 

 takes of the temperature of the atmosphere (up to 32^). The lower 

 stratum maintains a constant temperature of some eight degrees below 

 that of the underlying water. A fall of temperature, therefore, 

 affects only the upper stratum, while the lower stratum remains 

 unaffected. A separating and fracturing of the mass at its weakest 

 point must of course be the result. Just the contrary effect is pro- 

 duced when the upper stratum is affected by a high temperature ; 

 shoving and overlapping is the consequence. 



Ice, unlike most other solids, does not seem to possess the property 

 of contraction to the same extent as it does the power of expansion. 

 This will seem apparent from the following evidence : — When ice ex- 



