( 725 ) 



'2. In the deduction of formula (1) il was assumed that within 

 the layer of water the relation 



1 = o. 



<),■■ <i,r 



holds. Tins relation, however, holds for a body ai rest. Here, on 

 the other hand, we have to deal with a streaming liquid, in which 

 ease the following - formula holds : 



d*t d*t qS w ( dt dt 



dx' dy' 1 k 2 y d,v dy 



Here q is the specific heat of the liquid, u and v the velocity 

 components in the X- and Indirections. If we use this formula we 

 take into account that the heat, conducted through the wire, does 

 not entirely serve for melting the ice, hut that it is partly conveyed 

 upwards again by the streaming liquid. This also must result in 

 a diminution of the velocity of descent. Prof. Lorentz informed me, 

 however, that it can be shown that this influence must be regarded 

 as a quantity of the second order, so that the differences cannot be 

 explained in this way. 



3. If the temperature in the interior of the block of ice is not 

 exactly 0°, but lower, the velocity of descent will also become 

 smaller. But I observed no phenomena which point to a lower 

 temperature in the interior. Blocks of ice that had been kept for 

 24 hours in a space above 0° gave the same results as blocks that 

 had just been received. Moreover the wires as a rule went down 

 at a distance of only a few millimetres from one of the faces of 

 the block, and in some experiments they even came out of the block 

 by melting of that face. Yet in the last moment, before the wire 

 came out, no acceleration of the descent was observed. 



Nor does theory support such an explanation. Prof. Lorentz 

 informed me that when the surface of a ball of ice of 3 centimeters 

 diameter and at a temperature of — 2°, is raised to 0° and kept at 

 this temperature, it may be shown that in less than an hour the 

 temperature at the centre has risen to — 0.01°. 



4. Another important influence on the velocity of descent is found 

 in the fact that it is possible that not all the ice, melting at the 

 lower side of the wire, freezes again exactly at the upper side, but 

 that this water perhaps flow r s oil' laterally. It is clear that this must 

 have a great influence since then the heat, necessary for the melting, 

 is furnished by conduction through the ice. Already J. Thomson 



