1888.] On the Plasticity of Glacier and other Ice. 355 



Glacier Ice A. Length, between Needles, 22 cm. Tension 1*66 kilos. 



per sq. cm. 



Date. 



Tempera- 



Interval. 



Extension. 



Eate 

 per hour 

 per 10 cm. 



ture. 



Outer. 



Inner. 



Feb. 3, 9 h 



-2-5° 



hours. 



mm. 



mm. 



mm. 





-l'O 



3 *75 



yj — o 





*015 



„ „ 16 h. 30 m. , . . , 



-4-0 



3-75 



0-19 



o-oi 



0-013 



„ „ 21 h. 15 m 



o-o 



-3-0 



4-75 



35 



o-io 



0-022 



„ 4, 8 h. 30 m 



11-25 



0-53 



0-16 



0*014 





-1*0 



3-50 



0-19 



0'08 



0-018 













Total 





27-0 



1-49 



037 



0-0156 







interval. Tims the sixth column shows that the ice became more 

 plastic as it neared the thawing point. The unequal extensions in 

 the fourth and fifth columns may well have been due to eccentric 

 application of the tension. 



Experiment No. 6. Bough Apparatus. — The specimen was an icicle 

 trimmed with a knife to an uniform circular section. The apparatus 

 was greatly improved. The new mode of suspension was adopted, 

 specially arranged, as described above, to ensure the tension acting 

 along the central line of the bar. The indicators were hooked over 

 the top needle and bent at right angles so as to point downwards, as 

 in Main's apparatus. They were of glass, and no thoroughly efficient 

 means was taken to prevent slipping along the needle, but we do 

 not think any slipping can have taken place during the observations 

 quoted below. The whole apparatus was enclosed in a jacketed box — 

 which was, however, generally left open at night — and a centigrade 

 thermometer, graduated to tenths, was hung in the box on a level 

 with the middle of the ice. 



In the table the fourth and fifth columns give the actual extensions 

 during each interval, which may be trusted to 0*015 mm., and the 

 sixth column the mean rate of extension per hour per length of 

 10 cm. The second column gives the reading of the thermometer at 

 the time of the observation, and the last two columns the maximum 

 and mean temperatures of the ice during each interval. These are 

 tolerably accurate, as many observations were taken besides those 

 here quoted. The ice was not protected from evaporation, so the 



