National Geographic : 1892 Mar 21
Measurements of Ice-flow. Motion of the Ice. I had hoped to make an extended series of measurements of the motion at different parts of the glacier, but the pressure of other 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 crevassed, and in reaching the proper positions for planting the flags considerable difficulties were met; but, as in all such matters, this only added zest to theundertaking, and we set ourselves 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 yards apart, and although this interval is greater than we wished, still it is not much greater than the average interval between the flags; and so our series was practically continuous (see map of ice-front, plate 15). Two independent sets of measurements were 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 8, a period of 18 days, with a corresponding increase in accuracy in the determination of their daily rate. Three or four days was about as long as the flags would stand before falling, although they were planted in holes 18 inches deep. The flags marked with one dash belong to the first period, those with two dashes to the second; the others were observed during both. No results were obtained from 7', as it fell between July 21 and 24. The flags were observed from E and K, which were 5,513 yards apart, about three and one-quarter miles. These were the most avail able points of observation, and although they were not well adapted for determining with high accuracy the actual positions of the flags, still these positions were 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, however, was unimportant, for the direction is given by the moraines, which 7-NAT. GEOG.MAG., VOL.IV, 189'2.
1892 May 15
1892 Feb 19