In 1948 a steel tube was sunk into the Jungfraufin with a view to measuring the velocity distribution in the interior of the glacier.Footnote * In October 1949 M. André Roch and the writer carried out another set of inclinometer readings of the tube, using an improved type of inclinometer designed by Mr. Charles Jason.
The first results of the experiment are now available and are summarized in Fig. 1 below. Curves I and II show the position of the tube in August 1948 and October 1949, respectively. During that period the glacier surface advanced by 38 m. The curves demonstrate that the surface of the glacier travels fastest, and that the rate of flow decreases gradually towards the glacier bed. There is no evidence of extrusion flow. Figure 1b (curve III) which is a plot of the difference between curve II and I, shows the degree of bending of the tube. It is rigid to a depth of 50 m.; below this depth the curve is elliptical, with the greatest curvature near the glacier bed. The bottom 30 m. of curves I and III are drawn as dashed lines, because the first type of inclinometer, used in 1948, could not be lowered below 114 m. nor could its twist be controlled below 100 m. The original inclination of the tube below that depth is therefore uncertain.
Fig. 1. (a). The ordinates show depth, the abscissae the displacement, in metres. The arrow shows the direction of flow. Curve I gives the position of the steel tube on 15.8.48. curve II that on 10.10.49
Fig. 1 (b). Curve III is a plot of the differences between curves I and II
Fig. 2 Ordinates—Shear stress τ = Kg./cm.2 Abscissae—Creep rate 
cm. per cm. per day
The above results were used to calculate a tentative creep curve of ice (Fig. 2 above) with the rate of shear 
plotted as a function of the shear stress T. This curve shows the yield stress of ice at 0°C. to be certainly no more than 0.1 kg./cm 2 which is a tenth of the expected value. More accurate measurements carried out over a longer period may well prove that there is no detectable yield stress at all. On the other hand, the curve shows that creep only becomes really rapid at stresses approaching 1 kg./cm.2, so that perhaps, as a first approximation at any rate, ice may be regarded as an ideally plastic material with a yield stress of that order.Reference Orowan
1
It should be mentioned that the experiment was carried out at an altitude of 3350 m., where the boundary between firn and ice lies at about 19 m. depth,Reference Seligman 2 and where the entire glacier is at the pressure melting point, with the exception of a superficial crust of about 15 m. thickness which is penetrated by the winter cold wave.Reference Hughes and Seligman 3 A detailed account of this work will be published in due course.
