BucJdey — Ice Eamparts. 151 



cnmulate until the limit of elasticity is reached, Avhen relief will 

 take place. AVhenever the temperature of the ice is increased or 

 decreased forces will be set up tending to either expand or con- 

 tract the ice at the rate above given. 



During the month of February, 1900, the temperature of the 

 ice at different depths from the surface was obtained by using a 

 thermometer especially adapted for the purpose. Unfortun- 

 ately I was able to obtain only five sets of observations. These 

 indicate that the temperature of the ice at the surface, when 

 uncovered with snow, is about that of the atmosphere up to zero 

 centigrade, while it increases almost uniformly with the depth, 

 until the lower surface is reached, where the temperature is that 

 of unfrozen water. ^ From the observations taken, it appears 

 that the mean temperature of the ice is about midway between 

 the upper and lower surfaces and this can be taken as the aver- 

 age temperature of the ice sheet as a whole. 



As stated above the tensile stresses result from a lowering 

 temperature. These stresses are a maximum at the surface and 

 decrease with the increase in temperature as the under surface 

 of the ice is approached. The tensile stresses will be the same 

 for each unit of area in any one plane parallel to the surface and 

 different for every other plane. Each unit of a plane normal 

 to the surface, except those occurring in the same horizontal 

 plane as above stated, w^ill have stresses of different values. 

 That is to say, the tensile stresses are greatest at the surface and 

 decrease tow^ard the under surface of the ice sheet. If free to 

 move, the ice sheet would contract in all directions pai^i passu 

 with any decrease in temperature. However, the margin of the 

 ice sheet is attached to the shore in such a manner that im- 

 mediate contraction can only take place normal to the surface of 

 the ice sheet. The ice particles are free to move normal to the 

 surface of the sheet and the stresses in this direction, occasioned 

 by a lowering of the temperature, are immediately relieved by 

 the particles moving closer together. The contraction resulting 

 from stresses in this direction would not exceed one-twenty- 

 fourth of an inch for a thickness of thirty-five inches and a fall 



1 1 expect during another season to obtain a contiuuouf series of observations which 

 •will more fully demonstrate these conditions. 



