( ?13 ) 



the legs A and /) of an iron frame, which, in order to secure 

 greater rigidity, had been cui from an iron plate. In the lirst measure- 

 ments the downward displacements of the wire were observed by 

 means of a small reading telescope, turning round a horizontal and 



a vertical axis, and were determined on a measuring rod, mounted 

 at the side of the frame. The breadth of the ice-block was also read 

 on a horizontal measuring rod. In the later experiments a catheto- 

 meter was used, placed at my disposal by the professors of the 

 Technical university at Delft. I wish to express here my sincere 

 thanks to these gentlemen, especially to Prof. DE Haas. The fall of 

 the wire was always derived from the change in the difference of 

 level between the top of the wire and the upper edge of a small 

 bubble, existing somewhere in the interior of the ice. Every ten 

 minutes or, when the descent was quicker, every five minutes, the 

 difference of level was measured in order to ascertain whether the 

 fall was regular. Each experiment lasted 20 to 40 minutes. 



The ice used was artificial commercial ice. From a larger block 

 a clear smaller one was sawn out, in which some bubbles should be 

 present to serve as marks. The faces were melted flat by pressing 

 them against a metal plate, so that errors, caused by irregular 

 refraction, were avoided. 



Heat conduction along the wire was prevented by hanging small 

 pieces of ice on the wire on both sides of the block. Still small 

 grooves w T ere occasionally formed when the descent was slow. 



The experiments were made with wires of steel, german silver 

 and silver. The thickness of the wires was measured by means of 

 caliber compasses, giving results accurate to 0.01 mm. The thickness 

 was 0.5, 0.4 and 0.3 mm. Deviations from these numbers, amount- 

 ing to some hundredths of a millimetre, were occasionally found. 



For the case, realised in my experiments, in which the two straight 

 ends of the wire make a certain angle 2« with each other, formula 

 (lllrt) of Mr. Uknstein's paper : ) holds : 



2aCP 

 » = 3-r- (1) 



<f l S'/i (( 



in which r represents the velocity of descent of the wire, P the 

 total weight and (/ the breadth of the ice-block. C is a constant. 

 The value of this constant I calculated by formula (1) from the 

 values of v, found in my experiments. 



The results are summarised in the following table : 



i) 1. c. 



