EXPERIMENTS IN ICE MOTION. gIg 
as the class of obstructions it was desired to study would produce 
only this kind. The face of the obstructions extended entirely 
across the box and was rounded but quite abrupt. The inside 
of the boxes was planed smooth and then rubbed with olive oil 
to reduce friction and consequent drag on the sides (which it 
was feared would influence the results of the experiment) to as 
great an extent as possible. In experiments upon the effect of 
drag it was found necessary to increase it artificially. The 
boxes were fastened together by screws to facilitate handling. 
FIG. 1. 
In forcing the paraffine through the boxes the strength of the 
operator was generally found sufficient to produce the necessary 
rate of motion which did not exceed a foot in fifteen or twenty 
minutes and was, when necessary, further reduced by pauses in 
the operation. In order to trace the currents thin lines of pow- 
dered coal or galena and layers of darkened wax were used. 
When the wax was being packed in the box the different layers 
were fused on the surface with a Bunsen burner and allowed to 
stand in contact for a few moments before being moved in order 
to form a perfect union and regain a temperature similar to the 
residue of the wax. 
THE EXPERIMENTS. 
Experiment 1.—A box 6 by 6 inches and 12 inches long was 
furnished with an escarpment 1 inch high which extended to the 
rear of the box. Coarsely powered galena was sprinkled upon 
the floor of the box and the wax packed upon it. The wax was 
then subjected to ashove of about 3 inches. The result is 
shown in Fig. 1. 
