1888.] 



On the Plasticity of Glacier and other Ice. 



349 



on the micrometer scale of the cathetometer was taken twice, the 

 telescope having been turned about the vertical axis in the interim. 

 The two generally agreed. If not the mean was taken. On the 20fch, 

 however, a second set of readings was taken, the telescope having 

 been slid down the rod in the interim. Both determinations are 

 given. 



The errors of a cathetometer reading have been already discussed. 

 If we allow 0*11 mm. as a possible error in each determination of 

 the length, the observations are consistent with no real extension. 

 But taking the last two columns into consideration it seems probable 

 that there was an extension of 01 mm. between the 14th and 16th 

 and none later. Even if the total extension had been 0*2 mm., this 

 would have corresponded to a mean extension per hour per length of 

 10 cm. of only 0*0007 mm. 



'Experiment No. 2. — The same piece of ice was fitted up with glass 

 indicators and glass connecting fibres, the needles being the same as 

 before. Each indicator was provided with a mirror and scale set 

 close up to it, so readings on the scale could be taken to 0'2 mm. 

 But on the other hand there was a possibility of the indicators 

 slipping on the needles and thus occasioning a slight apparent con- 

 traction. The multiplication on the outer side was 34, on the 

 inner 26. Thus an extension of 0*007 mm. could be detected. The 

 second, third, and fourth columns of the following table give the 

 extensions, measured from the length at the time of the third 

 observation (for a reason mentioned below), and reduced to the pro- 

 portionate amount for a length of 10 cm. They are probably correct to 

 0*004 mm. 



Experiment No. 2. — Main's Apparatus. Bath Ice. Length between 

 Needles 16 cm. Tension 4*9 kilos, per square centimetre. 



Date. 



Extension per 10 cm. 



Outer. 



Inner. 



Mean. 



Temperature 

 at the time. 



Jan. 



Feb. 



mm. 



mm. 



10 h. 30 m. 

 16 h. 30 m 



9h. 15 m. 

 16 h. 30 m 



9 h. 30 m. 



>> j> 

 16 h 



9 h. 45 m. 



12 h 



18 h. 10 m. 



9 h. 30 m. 

 16 h 





 

 



-0 

 



-0 

 

 

 

 

 

 



•016 

 •016 

 •000 

 •002 



•ooo 



•002 

 •007 

 •007 

 •009 

 •007 

 •007 

 •007 



•000 

 •055 

 •000 

 •000 

 019 

 •002 

 •022 

 •022 

 •045 

 •050 

 •048 

 •043 



•008 

 •035 

 •000 

 •001 

 •009 

 •000 

 •014 



014 

 •027 

 •028 



027 

 •027 



5 



•o° 



15 







12 



•5 



8 



•5 



8 



•8 



6 



4 



6 



•5 



3 



•7 



1 



6 



1 



5 



1 







