Measurements of Ice-fow. 43 



Jkitinri of the Ice. 



I had hoped to make an extended series of uieasurenients of 

 the motion at different parts of the glacier, bnt the pressure of 

 otlaer work and the great extent of the ice forced us to be con- 

 tent with a measure of the motion near the mouth. The reported 

 motion of 70 feet a day was so great that we felt that careful pre- 

 cautions must be taken to avoid all error. We determined not 

 to trust to sighting on pinnacles, but to set out a series of flags 

 whose identity could not be mistaken. The middle part of the 

 glacier is deeply creyassed, and in reacliing the proper positions 

 for planting the flags considerable difficulties Avere met ; but, as 

 in all such matters, tliis only added zest to the undertaking, and 

 we set ourselyes to the task of crossing the ice near its end. In 

 this we were unsuccessful, although when setting out the flags 

 we made five or six attempts, first from one side and then from 

 the other. The furthest points reached from opposite sides were 

 about 500 3^ards apart, and although this interval is greater than 

 we wished, still it is not much greater than the average interval 

 between tlie flags ; and so our series was y)ractically continuous 

 (see map of ice -front, })late 15). 



Two independent sets of measurements Avere made, the first 

 on a series of ten flags from July 21 to 24, the second on a series 

 of nine flags from August 4 to 8. The first three flags on each 

 side were recovered after the first set of observations and replaced, 

 so that observations on them extended from July 21 to August 

 S, a period of 18 days, with a corresponding increase inaccuracy 

 in the determination of their daily rate. Three or four days was 

 about as long as the flags Avould stand before falling, altliough 

 they Avere planted in holes 18 inches deep. The flags marked 

 Avith one dash belong to the first period, those Avith two dashes 

 to the second ; the others Avere observed during both. No results 

 Avere obtained from 7', as it fell betAveen July 21 and 24. The 

 flags Av ere observed from £* and A", Avhich Avere 5,51B yards apart, 

 about three and one-quarter miles. These Avere the most aA^ail- 

 able points of observation, and altliough they Avere not Avell 

 adapted for determining Avith high accuracy the actual positions 

 of the flags, still these positions Avere determined with quite suffi- 

 cient precision. The direction of the motions could not be de- 

 termined from our observations, for very small errors of observa- 

 tion produce large errors in this direction. This, hoAvever, Avas 

 unimportant, for the direction is given by the moraines, Avhicli 



7— Nat. Gkoo. Mac, vol. IV, 1892. 



