Early in the 19th century, the first experiments involving the movement of glaciers were designed and carried out in the Alps. Markers were placed in a straight line across an alpine glacier.
The position of the line was marked on the valley walls so that if the ice moved, the change in position could be detected. Periodically the positions of the markers were noted, revealing the movement just described.
Although most glaciers move too slowly for direct visual detection, the experiments succeeded in demonstrating that movement nevertheless occurs.
The experiment illustrated was carried out at Switzerland's Rhone Glacier later in the 19th century It not only traced the movement of markers within the ice but also mapped the position of the glacier's terminus.